Shaped optical films and methods of shaping optical films

ABSTRACT

Optical films having a curved shaped and methods of shaping optical films are described. A method of shaping an optical film includes the steps of disposing the optical film adjacent first and second rollers spaced apart along a first direction, securing opposing first and second ends of the optical film, providing a curved mold surface, and shaping the optical film by contacting the optical film with the curved mold surface while stretching the optical film along the first direction and keeping a threshold distance between closest points on the optical film contacting the first roller and contacting the curved mold surface less than the width of the optical film to reduce buckling of the optical film.

BACKGROUND

An optical film can be thermoformed into a curved shape.

SUMMARY

In some aspects of the present description, a method of shaping anoptical film is provided. The method includes the steps of: disposingthe optical film adjacent first and second rollers such that a firstportion of the optical film contacts the first roller and a secondportion of the optical film contacts the second roller, where the firstand second rollers are spaced apart along a first direction and thefirst portion of the optical film has a first width along a seconddirection orthogonal to the first direction; securing opposing first andsecond ends of the optical film, where the first and second ends arespaced apart along the first direction and the first and second portionsare disposed between the first and second ends; providing a curved moldsurface; and shaping the optical film by contacting the optical filmwith the curved mold surface while stretching the optical film along thefirst direction. The shaping step includes keeping a threshold distancebetween closest first and second points less than about the first widthwhere the first point on the optical film contacts the first roller andthe second point on the optical film contacts the curved mold surface.

In some aspects of the present description, a method of shaping anoptical film is provided. The method includes the steps of: disposingthe optical film adjacent first and second rollers such that a firstportion of the optical film contacts the first roller and a secondportion of the optical film contacts the second roller, where the firstand second rollers spaced are apart along a first direction and thefirst portion of the optical film has a first width along a seconddirection orthogonal to the first direction; securing opposing first andsecond ends of the optical film where the first and second ends arespaced apart along the first direction and the first and second portionsare disposed between the first and second ends; providing a curved moldsurface; and shaping the optical film by contacting the optical filmwith the curved mold surface while stretching the optical film along thefirst direction. The shaping step includes changing a separationdistance between the first and second rollers along the first directionto reduce buckling of the optical film between the first and secondrollers and along the second direction between and away fromlongitudinal edges of the optical film.

In some aspects of the present description, a method of shaping anoptical film is provided. The method includes the steps of: securingopposing first and second ends of the optical film where the first andsecond ends are spaced apart along a first direction; securing opposingthird and fourth ends of the optical film where the third and fourthends are spaced apart along a second direction orthogonal to the firstdirection; providing a curved mold surface; and shaping the optical filmby contacting the optical film with the curved mold surface whilestretching the optical film, resulting in a curved optical film curvedalong at least the first direction. Stretching the optical film duringthe shaping step includes stretching the optical film along the firstdirection greater than 3 times any stretching along the seconddirection.

In some aspects of the present description, a curved optical filmincluding a plurality of polymeric layers shaped along orthogonal firstand second directions is provided. A first curve being an intersectionof the optical film with a first plane orthogonal to the seconddirection and to a reference plane has a best-fit first circular arcsubtending a first angle at a center of curvature of the first circulararc of greater than 180 degrees where the optical film has a maximumprojected area in the reference plane. A second curve being anintersection of the optical film with a second plane orthogonal to thefirst direction and to the reference plane has a best-fit secondcircular arc subtending a second angle at a center of curvature of thesecond circular arc of at least 30 degrees. Each location across atleast 90% of a total area of the optical film has a reflectance greaterthan about 80% and a transmittance less than about 2% for normallyincident light having a same predetermined wavelength and a same firstpolarization state.

In some aspects of the present description, a curved optical filmincluding a plurality of polymeric layers shaped along orthogonal firstand second directions is provided. A first curve being an intersectionof the optical film with a first plane orthogonal to the seconddirection and to a reference plane has a best-fit first circular arcsubtending a first angle at a center of curvature of the first circulararc of at least 90 degrees where the optical film has a maximumprojected area in the reference plane. A second curve being anintersection of the optical film with a second plane orthogonal to thefirst direction and to the reference plane has a best-fit secondcircular arc subtending a second angle at a center of curvature of thesecond circular arc of at least 30 degrees. Each location across atleast 90% of a total area of the optical film has a reflectance greaterthan about 80% and a transmittance less than about 2% for normallyincident light having a same predetermined wavelength and a same firstpolarization state. The first curve passes through a center of theoptical film. The optical film has a first thickness at a first locationalong the first curve and a second thickness at a second location alongthe first curve, where the second location is separated from the firstlocation by a distance along the first curve of at least 0.7 times aradius R1 of the best-fit first circular arc, a distance from the centerof the optical film to the first location along the first curve is nomore than 0.2 R1, and a distance from the second location to an edge ofthe optical film along the first curve being no more than 0.2 R1. Thefirst and second thicknesses differ by no more than 5%.

In some aspects of the present description, a curved optical filmincluding a plurality of polymeric layers shaped along orthogonal firstand second directions is provided. A first curve being an intersectionof the optical film with a first plane orthogonal to the seconddirection and to a reference plane has a best-fit first circular arcsubtending a first angle at a center of curvature of the first circulararc of at least 90 degrees where the optical film has a maximumprojected area in the reference plane. A second curve being anintersection of the optical film with a second plane orthogonal to thefirst direction and to the reference plane has a best-fit secondcircular arc subtending a second angle at a center of curvature of thesecond circular arc of at least 30 degrees. Each location across atleast 90% of a total area of the optical film has a reflectance greaterthan about 80% and a transmittance less than about 2% for normallyincident light having a same predetermined wavelength and a same firstpolarization state. The first curve passes through a center of theoptical film. The optical film has a first long wavelength band edge ata first location along the first curve and a second long wavelength bandedge at a second location along the first curve, where the secondlocation is separated from the first location by a distance along thefirst curve of at least 0.7 times a radius R1 of the best-fit firstcircular arc, a distance from the center of the optical film to thefirst location along the first curve is no more than 0.2 R1, and adistance from the second location to an edge of the optical film alongthe first curve being no more than 0.2 R1. The first and second longwavelength band edges differ by no more than 5%.

In some aspects of the present description, an optical film including aplurality of polymeric layers is provided. Each location across at least90% of a total area of the optical film has a reflectance greater thanabout 80% and a transmittance less than about 5% for normally incidentlight having a same predetermined wavelength and a same firstpolarization state. For orthogonal first and second planes intersectingthe optical film along respective first and second curves where thefirst and second curves intersect each other at a center location of theoptical film, the optical film has a thickness that decreases from thecenter location to a first edge location of the optical film along thefirst curve and increases from the center location to a second edgelocation along the second curve.

In some aspects of the present description, an optical film including aplurality of polymeric layers is provided. Each location across at least90% of a total area of the optical film has a reflectance greater thanabout 80% and a transmittance less than about 5% for normally incidentlight having a same predetermined wavelength and a same firstpolarization state. For orthogonal first and second planes intersectingthe optical film along respective first and second curves where thefirst and second curves intersect each other at a center location of theoptical film, the optical film has a long wavelength band edge thatdecreases from the center location to a first edge location of theoptical film along the first curve and increases from the centerlocation to a second edge location along the second curve.

In some aspects of the present description, an optical film including aplurality of polymeric layers is provided. Each location across at least90% of a total area of the optical film having a reflectance greaterthan about 80% and a transmittance less than about 5% for normallyincident light having a same predetermined wavelength and a same firstpolarization state. For orthogonal first and second planes intersectingthe optical film along respective first and second curves, the opticalfilm has a first thickness distribution along the first curve that issubstantially symmetric under reflection about the second plane and asecond thickness distribution along the second curve that issubstantially symmetric under reflection about the first plane, thefirst and second thickness distributions being different.

In some aspects of the present description, an optical film including aplurality of polymeric layers is provided. Each location across at least90% of a total area of the optical film having a reflectance greaterthan about 80% and a transmittance less than about 5% for normallyincident light having a same predetermined wavelength and a same firstpolarization state. For orthogonal first and second planes intersectingthe optical film along respective first and second curves, the opticalfilm has a first long wavelength band edge distribution along the firstcurve that is substantially symmetric under reflection about the secondplane and a second long wavelength band edge distribution along thesecond curve that is substantially symmetric under reflection about thefirst plane, the first and second long wavelength band edgedistributions being different.

In some aspects of the present description, a curved reflectivepolarizer including a plurality of polymeric layers shaped along atleast orthogonal first and second directions is provided. A first ratioof a first maximum sag to a corresponding first diameter along the firstdirection is at least 0.1, and a second ratio of a second maximum sag toa corresponding second diameter along the second direction is at least0.05. For normally incident light in a predetermined wavelength range,each location on the reflective polarizer has a maximum averagereflectance greater than about 80% and a corresponding minimum averagetransmittance less than about 2% for a block polarization state, and amaximum average transmittance greater than about 80% for an orthogonalpass polarization state. Each location in a region of the reflectivepolarizer having an area of at least 80% of a total area of thereflective polarizer has a contrast ratio being the maximum averagetransmittance divided by the minimum average transmittance of at least500.

In some aspects of the present description, a curved reflectivepolarizer including a plurality of polymeric layers shaped alongorthogonal first and second directions is provided. A total curvature ofthe reflective polarizer is at least 0.25 where the total curvature is asurface integral of a Gaussian curvature of the reflective polarizerover a total area of the reflective polarizer. For normally incidentlight in a predetermined wavelength range, each location on thereflective polarizer has a maximum average reflectance greater thanabout 80% and a corresponding minimum average transmittance less thanabout 2% for a block polarization state, and a maximum averagetransmittance greater than about 80% for an orthogonal pass polarizationstate. Each location in a region of the reflective polarizer having anarea of at least 80% of the total area of the reflective polarizer has acontrast ratio being the maximum average transmittance divided by theminimum average transmittance of at least 500.

In some aspects of the present description, a curved reflectivepolarizer including a plurality of polymeric layers shaped along atleast orthogonal first and second directions is provided. A first ratioof a first maximum sag to a corresponding first diameter along the firstdirection is at least about 0.1, and a second ratio of a second maximumsag to a corresponding second diameter along the second direction is atleast about 0.05. For normally incident light having a predeterminedwavelength, each location over at least 80% of a total area of thereflective polarizer has a maximum reflectance greater than about 80%and a corresponding minimum transmittance less than about 0.2% for ablock polarization state, and a maximum transmittance greater than about80% for an orthogonal pass polarization state.

In some aspects of the present description, a curved reflectivepolarizer including a plurality of polymeric layers shaped alongorthogonal first and second directions is provided. A total curvature ofthe reflective polarizer is at least 0.25 where the total curvaturebeing a surface integral of a Gaussian curvature of the reflectivepolarizer over a total area of the reflective polarizer. For normallyincident light having a predetermined wavelength, each location over atleast 80% of a total area of the reflective polarizer has a maximumreflectance greater than about 80% and a corresponding minimumtransmittance less than about 0.2% for a block polarization state, and amaximum transmittance greater than about 80% for an orthogonal passpolarization state.

In some aspects of the present description, an apparatus for processingoptical film is provided. The apparatus includes: first and secondrollers spaced apart along a first direction and disposed on respectivefirst and second stages configured to move the first and second rollersalong the first direction, where the first and second rollers haverespective first and second widths along a second direction orthogonalto the first direction; first and second securing means for securingopposing first and second ends of the optical film, where the first andsecond rollers are disposed between the first and second securing meansand the apparatus is configured such that when the first and second endsof the optical film are secured in the first and second securing means,the optical film contacts the first and second rollers; a mold having acurved mold surface and disposed on a mold stage configured to move themold along a third direction orthogonal to the first and seconddirections; a means for heating the optical film; a tension measuringmeans for measuring a tension in the optical film; a controllercommunicatively coupled to the tension measuring means, the first andsecond stages, the first and second securing means, and the mold stage.The controller is configured to simultaneously move the mold along thethird direction and move the first and second roller along the firstdirection while controlling the tension in the optical film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1E are schematic illustrations of a method of shaping opticalfilms;

FIGS. 2-3 are schematic side views of steps in methods of shapingoptical films;

FIG. 4A is a schematic side view of an apparatus for shaping an opticalfilm;

FIG. 4B is a schematic side view of a heating means and a lens mountdisposed on a stage;

FIG. 5A is a side view of an apparatus for shaping an optical film;

FIG. 5B is a perspective view of the apparatus of FIG. 5A;

FIG. 6-7 are schematic top views of molds disposed over optical films;

FIG. 8A is a schematic top view of a portion of an optical filmexhibiting buckling;

FIG. 8B is a schematic cross-sectional view through buckles in theoptical film of FIG. 8A;

FIG. 8C is a schematic front plan view of an optical film illustrating apredetermined region of the optical film;

FIGS. 9A-9B are schematic cross-sectional views of an optical film inorthogonal planes;

FIG. 10A-10C are schematic perspective views of an optical film;

FIG. 11A is a schematic illustration of a first curve and a best-fitfirst circular arc;

FIG. 11B is a schematic illustration of a second curve and a best-fitsecond circular arc;

FIGS. 11C-11D are schematic plots of possible thickness profiles alongthe first curve of FIG. 11A;

FIG. 11E is a schematic plot of a possible thickness profile along thesecond curve of FIG. 11B;

FIGS. 11F-11G are schematic plots of possible long wavelength band edgeprofiles along the first curve of FIG. 11A;

FIG. 11H is a schematic plot of a possible long wavelength band edgeprofile along the second curve of FIG. 11B;

FIG. 12 is a schematic side-view of a mold;

FIG. 13 is a schematic cross-sectional view an optical film;

FIG. 14 is a schematic front plan view of an optical film;

FIGS. 15A-15B are schematic illustrations of first and second thicknessdistributions;

FIGS. 15C-15D are schematic illustrations of first and second long bandwidth edge distributions;

FIG. 16 is a schematic plot of the transmittance of a reflectivepolarizer for pass and block states;

FIG. 17 is a schematic plot of the reflectance of a reflective polarizerfor pass and block states;

FIGS. 18A-18B are schematic cross-sectional views of optical films;

FIG. 19 is a plot of a layer thickness versus layer number for anoptical film;

FIG. 20A is a schematic cross-sectional view of a portion of an opticalfilm disposed on a curved mold surface proximate an optical lens;

FIG. 20B is a schematic cross-sectional view of a lens assembly;

FIG. 21A is a schematic illustration of a lens mount holding an opticallens with an optical film disposed on the optical lens;

FIG. 21B is a schematic cross-sectional view of a lens assembly;

FIG. 22A-22B are plots of thickness distributions of films shaped usingpulldown and pressurization processes;

FIG. 23A-23B are images of molds;

FIG. 24 is a schematic top view of a reflective polarizer;

FIG. 25 is a plot of average block state transmissions of reflectivepolarizers;

FIG. 26 is a plot of average pass state transmissions of reflectivepolarizers;

FIG. 27 is a plot of contrast ratios of reflective polarizers;

FIG. 28 is a plot of long wavelength band edges of reflectivepolarizers;

FIG. 29 is a contour plot of the average block state transmission of areflective polarizer;

FIG. 30 is a contour plot of the average pass state transmission of areflective polarizer;

FIG. 31 is a contour plot of the contrast ratio of a reflectivepolarizer;

FIG. 32 is a plot of the half wrap length of an optical film on a moldas a function of time during a shaping process for various processconditions;

FIG. 33 is a plot of the span length of an optical film between acontact point on a mold and a contact point a roller as a function oftime during a shaping process for various process conditions;

FIG. 34 is a plot of the tension along the length of an optical film asa function of time during a shaping process for various processconditions;

FIGS. 35-38 are plots of the thickness distribution of shaped opticalfilms for various process conditions.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingdrawings that form a part hereof and in which various embodiments areshown by way of illustration. The drawings are not necessarily to scale.It is to be understood that other embodiments are contemplated and maybe made without departing from the scope or spirit of the presentdescription. The following detailed description, therefore, is not to betaken in a limiting sense.

According to some aspects of the present description, methods of shapingan optical film are provided. In some embodiments, the methods of thepresent description allow an optical film to be formed into shapes thatwould be difficult to achieve using conventional thermoformingtechniques while maintain desired optical properties over most or all ofthe optical film. For example, an optical film can be curved to subtendan angle at a center of curvature of the optical film that is greaterthan 180 degrees. In some embodiments, the methods of the presentdescription provide a thickness variation of the optical film that isdifferent from that of optical films thermoformed by conventionalmethods. For example, the thickness may increase from a center of theoptical film along one axis and decrease from the center along anorthogonal axis. As another example, the thickness may varynon-monotonically from a center of the optical film to an edge of theoptical film along at least one direction. In some embodiments, theoptical film is a reflective polarizer and the methods of the presentdescription allow substantially more stretching of the reflectivepolarizer along a block axis than along a pass axis during the shapingof the reflective polarizer and this has been found to decrease thetransmittance of light polarized along the block axis and increase thecontrast ratio of the reflective polarizer.

The optical films of the present description may include a plurality ofalternating polymeric layers and may transmit and reflect lightprimarily by optical interference. In some embodiments, the optical filmis a mirror film and in some embodiments, the optical film is areflective polarizer. In either case, each location over at least 80% ofa total area of the shaped optical film may have a reflectance greaterthan about 80% for normally incident light having a same predeterminedwavelength and a same first polarization state. In the case of areflective polarizer, the transmittance for normally incident lighthaving the predetermined wavelength and a same orthogonal secondpolarization state may be greater than 80% at each location over atleast 80%, or at least 85%, or at least 90%, or at least 95% of thetotal area of the shaped optical film. In some embodiments, thepredetermined wavelength is a wavelength in predetermined wavelengthrange.

The predetermined wavelength range may be the wavelength range overwhich an optical system including the optical film is designed tooperate. For example, the predetermined wavelength range may be thevisible range (400 nm to 700 nm) or a substantial subset of the visiblerange (e.g., 450 nm to 650 nm). As another example, the predeterminedwavelength range may include one or more visible wavelength ranges. Forexample, the predetermined wavelength range may be the union of morethan one narrow wavelength ranges (e.g., the union of disjoint red,green and blue wavelength ranges corresponding to light emission colorsof a display panel). Such wavelength ranges are described further inU.S. Pat. Appl. Pub. No. 2017/0068100 (Ouderkirk et al.), which ishereby incorporated herein by reference to the extent that it does notcontradict the present description. In some embodiments, thepredetermined wavelength ranges include other wavelength ranges (e.g.,infrared (e.g., near infrared (about 700 nm to about 2500 nm)), orultraviolet (e.g., near ultraviolet (about 300 nm to about 400 nm)) aswell as visible wavelength ranges. For example, the optical film may bean infrared reflector and the predetermined wavelength range may be anear infrared range. A predetermined wavelength may be any wavelength inthe predetermined wavelength range. For example, a predeterminedwavelength range may be from 400 nm to 700 nm and the predeterminedwavelength may be 500 nm or 550 nm, for example.

A method of shaping an optical film according to the present descriptionis illustrated in FIGS. 1A-1E. FIG. 1A is a schematic cross-sectionalview of an optical film 100 disposed adjacent first and second rollers20 and 25 such that a first portion 120 of the optical film 100 contactsthe first roller 20 and a second portion 125 of the optical film 100contacts the second roller 25. FIG. 1B is a top schematic view of thesystem of FIG. 1A. The first and second rollers 20 and 25 are spacedapart along a first direction 50 (parallel to x-direction). The firstportion 120 of the optical film 100 has a first width W1 along a seconddirection 67 (parallel to y-direction) orthogonal to the first direction50. The first roller 20 has a first width WR1 along the second direction67. In some embodiments, the width WR1 is greater than the width W1. Thesecond portion 125 of the optical film 100 has a second width W2 alongthe second direction 67. The second roller 25 has a second width WR2along the second direction 67. In some embodiments, the width WR2 isgreater than the width W2. In some embodiments, W1 and W2 are equal orabout equal. In some embodiments, the optical film has a substantiallyconstant width (e.g., no more than 10% variation) that is about equal toW1 and to W2. In some embodiments, WR1 and WR2 are equal or about equal.

The method comprises securing the first and second ends 101 and 102 ofthe optical film 100. In the illustrated embodiment, securing means 30and 35 are used to secure the first and second ends 101 and 102. Thesecuring means 30 and 35 may be or include claps, grips or a roller(e.g., a Capstan roller) and may be configured to move along the firstdirection 50. The first and second ends 101 and 102 are spaced apartalong the first direction 50 with the first and second portions 120 and125 disposed between the first and second ends 101 and 102.

Mold 250 has a curved mold surface 255. The mold 250 has a length L1along the first direction 50 and a length L2 along the second direction67. The curved mold surface may have the same or similar lengths alongthe first and second directions. The optical film 100 may have a width(e.g., W1 and/or W2) that is larger than L2 as illustrated in FIG. 1B.In this case, a portion of the optical film 100 may be cut out afterforming into a desired shape to remove edges which were not formed. Inother embodiments, an optical film 100 b, which may be used in place ofoptical film 100, may have a width (e.g., W1 and/or W2) that is smallerthan L2 as illustrated in FIG. 1C. In some embodiments, the width of theoptical film is about equal to the length L2 of the mold 250 along thesecond direction 67. Mold 250 includes optional heating element(s) 253which may be used to heat the mold. The optional heating element(s) 253may be disposed within the mold 250 or on a surface of the mold, forexample. In some embodiments, the mold 250 is heated to a temperaturehigher than ambient temperature. For example, in some embodiments, themold 250 is heated to a temperature greater than 30° C., or greater than40° C. In some embodiments, the optical film 100 is heated to apredetermined temperature prior to shaping the optical film 100. In someembodiments, the mold 250 is heated to a temperature that is less thanthis predetermined temperature.

In some embodiments, the optical film 100 is shaped by contacting theoptical film 100 with the curved mold surface 255 while stretching theoptical film 100 along the first direction 50. This can be done bymoving the mold 250 towards the optical film 100 along a third direction75 (parallel to z-direction) orthogonal to the first and seconddirections 50 and 67 until the curved mold surface 255 contacts theoptical film and continuing to move the mold 250 until the optical film100 conforms to at least a portion of the curved mold surface 255. Thiscan be described as changing a separation distance h between a point 257on a boundary of the curved mold surface 255 and the optical film 100along the third direction 75. The boundary of the curved mold surface255 can be taken to be a physical boundary where the curvature changesabruptly if such a boundary is present or the boundary may be taken tobe a boundary of the maximum area of the curved mold surface which makescontact with the optical film 100 during the shaping of the optical film100. FIG. 1D is a schematic cross-sectional view of a step in theshaping method where the mold 250 has initially contacted the opticalfilm 100 and FIG. 1E is a schematic cross-sectional view of a time inthe shaping method after a continuous portion of the optical film 100has contacted the curved mold surface 255. In the illustratedembodiment, the securing means 30 and 35 are positioned lower (smallerz-coordinate) than the first and second rollers 20 and 25. In otherembodiments, when the mold 250 initially contacts the optical film 100,the securing means 30 and 35 are positioned so that the span of filmbetween the securing means 30 and the mold 250, the span of film betweenthe securing means 35 and the mold 250, and the span of film between thefirst and second rollers 20 and 25 are parallel to one another.

In some embodiments, a temperature of the optical film is lower at afirst point of the optical film contacting the curved mold surface(e.g., point 134 or point 135) than at a second point of the opticalfilm not contacting the curved mold surface (e.g., a point halfwaybetween point 135 and point 136, or a point halfway between point 133and point 134).

The shaping of the optical film 100 preferably comprises keeping athreshold distance d1 between closest first and second points 133 and134 less than about the first width W1, where the first point 133 on theoptical film 100 contacts the first roller 20, and the second point 134on the optical film 100 contacts the curved mold surface 255. In otherwords, d1 is the smallest distance between any point on the optical film100 contacting the first roller 20 and any point on the optical film 100contacting the curved mold surface 255, and the method of shaping theoptical film 100 includes keeping d1 less than about W1. In someembodiments, the shaping of the optical film 100 further compriseskeeping a threshold distance d2 between closest third and fourth points135 and 136 less than about the second width W2, where the third point135 on the optical film 100 contacts the curved mold surface 255, andthe fourth point 136 on the optical film 100 contacts the second roller25. In other words, d2 is the smallest distance between any point on theoptical film 100 contacting the curved mold surface 255 and any point onthe optical film 100 contacting the second roller 25, and the method ofshaping the optical film 100 includes keeping d2 less than about W2.Keeping d1 and/or d2 in a desired range typically comprises moving thefirst and/or second rollers 20 and/or 25 along the first direction 50.In preferred embodiments, the first and second rollers 20 and 25 aremoved along the first direction 50 so that the distance d between thefirst and second rollers 20 and 25 changes during the shaping of theoptical film 100 to keep both d1 and d2 in the desired ranges. In someembodiments, one or more or all of the first, second, third, and fourthpoints 133, 134, 135, and 136 moves along the first direction 50 as theoptical film 100 is shaped.

Without the first and second rollers 20 and 25, the optical film 100 (or100 b) would typically buckle along the second direction 67 in theregion 73 (or 73 b). It has been found that including the first andsecond rollers 20 and 25 and keeping d1 and/or d2 in a desired range canreduce or eliminate buckling of the optical film in the seconddirection. Friction between the optical film 100 (or 100 b) and thefirst and second rollers 20 and 25 can result in positive tension in theoptical film 100 (or 100 b) along the second direction and this tensioncan prevent buckling. In some embodiments, the first and second rollers20 and 25 have a smooth surface. In some embodiments, the first andsecond rollers 20 and 25 are spreader rollers. Spreader rollers includegrooves, for example, which can result in increased tension in theoptical film 100 (or 100 b) along the second direction 67. Spreaderrollers are known in the art and are described in U.S. Pat. No.6,843,762 (Munche et al.), for example.

In some embodiments, the threshold distance d1 is kept at no more thanW1, or no more than 0.9 W1, or no more than 0.8 W1, or no more than 0.7W1, or no more than 0.6 W1, or no more than 0.5 W1, or no more than 0.4W1, or no more than 0.3 W1. In some embodiments, the threshold distanced1 is kept at at least 0.001 W1, or at least 0.01 W1, or at least twicea thickness t of the optical film 100 (or 100 b), or at least 5 timesthe thickness, or at least 10 times the thickness. In some embodiments,the threshold distance d2 is kept at no more than W2, or no more than0.9 W2, or no more than 0.8 W2, or no more than 0.7 W2, or no more than0.6 W2, or no more than 0.5 W2, or no more than 0.4 W2, or no more than0.3 W2. In some embodiments, the threshold distance d1 is kept at atleast 0.001 W2, or at least 0.01 W2, or at least twice a thickness ofthe optical film 100 (or 100 b), or at least 5 times the thickness, orat least 10 times the thickness.

In some embodiments, the threshold distances d1 and d2 are independentlycontrolled. In some embodiments, the first and second rollers 20 and 25are disposed substantially symmetrically about the mold 250 so that d1is equal to or about equal to d2. In other embodiments, the first andsecond rollers 20 and 25 are disposed asymmetrically about the mold 250so that d1 and d2 are different. In some cases, this may be done tofacilitate shaping the optical film 100 into an asymmetric shape (e.g.,a teardrop shape).

In some embodiments, the shaping of the optical film 100 (or 100 b)comprises changing a separation distance d between the first and secondrollers 20 and 25 along the first direction 50 to reduce buckling of theoptical film 100 (or 100 b) in the region 73 (or 73 b) between the firstand second rollers 20 and 25 and along the second direction 67 betweenand away from longitudinal edges 71 and 72 (or 71 b and 72 b) of theoptical film 100 (or 100 b). In some cases, buckling along thelongitudinal edges 71 and 72 can be acceptable since the buckling may besubsequently removed and/or portions of the optical film along thelongitudinal edges 71 and 72 may be removed prior to using the shapedoptical film in an optical system, for example.

The first and second securing means 30 and 35 may configured to movealong the first direction 50. In some embodiments, the positions of thefirst and second ends 101 and 102 are changed to control the tension inthe optical film 100 (or 100 b) along the first direction 50. Thepositions of the first and second ends 101 and 102 can be changed bymoving the first and second securing means 30 and 35 along the firstdirection 50. Alternatively, the first and second securing means 30 and35 may be rollers where the ends of the films are secured on or in therollers and the tension in the first direction 50 can be changes byrotating the rollers. In this case, the positions of the first andsecond ends 101 and 102 may be change due to the rotation of therollers. In some embodiments, the tension in the optical film 100 (or100 b) along the first direction 50 is substantially constant as thefilm is stretched. The tension may be described as substantiallyconstant or substantially unchanged if it varies by no more than 10%over at least 90% of the time that the optical film is being shaped. Insome embodiments, the tension in the optical film 100 along the firstdirection 50 gradually increases during the stretching of the opticalfilm 100. In some embodiments, the tension is controlled to produce adesired thickness variation in the optical film. For example, thedesired thickness may be substantially constant along the firstdirection 50. As another example, the desired thickness distribution maybe generally decreasing from a center of the optical film to each ofopposing edges along the first direction 50. The reflection band edgesof the optical film are typically proportional to the thickness. Adesired band edge distribution may determine the desired thicknessdistribution, for example.

In some embodiments, the optical film 100 (or 100 b) is heated. In someembodiments, the heating may be carried out prior to and optionallyduring stretching of the optical film 100. The heating can utilize oneor more of infrared (IR) heating, convection heating and radiativeheating. FIG. 1A schematically shows a heater 91 disposed to heat theoptical film 100. The heater 91 is disposed on a side of the opticalfilm 100 opposite the curved mold surface 255. In some embodiments, theheater 91 is an infrared heater. In some embodiments, an infraredreflective surface is disposed proximate the optical film opposite theinfrared heater. For example, in some embodiments, the curved moldsurface 255 is an infrared reflective surface which is positionedproximate the optical film 100 during the heating of the optical film100. In other embodiments, a separate infrared reflector is disposedbetween the curved mold surface 255 and the optical film 100 during theheating of the optical film 100. The separate infrared reflector is thenremoved prior to the shaping of the optical film 100.

In some embodiments, the optical film 100 (or 100 b) is heated to atemperature in a range of 120° C. to 200° C., or in a range of 160° C.to 200° C. In some embodiments, the optical film 100 is heated to atemperature greater than a glass transition temperature of the opticalfilm 100. In some embodiments, the mold 250 is heated prior to and/orduring the shaping of the optical film 100. For example, the mold 250may be heated to a temperature greater than 30° C. Prior to shaping, thetemperature of the mold 250 may be lower than the temperature of theoptical film 100. In some embodiments, the temperature of the opticalfilm 100 during the shaping step is lowest at a point of the opticalfilm contacting an apex of the curved mold surface 255 and higher inportions of the optical film 100 not contacting the curved mold surface255. In some embodiments, during the shaping step, a temperature of theoptical film 100 changes from a midpoint of the optical film 100 betweenthe first and second rollers toward each of the first and secondrollers. In some embodiments, during the shaping step, the temperatureof the optical film 100 changes from a midpoint between the longitudinaledges 71 and 72 and between the first and second rollers 20 and 25toward each longitudinal edge. The midpoint of the optical film 100 maybe the point which contacts the apex of the curved mold surface 255. Insome embodiments, the first and second rollers 20 and 25 are also heated(e.g., to a temperature greater than 30° C.). Third and fourth rollersdescribed elsewhere herein may also be heated.

The glass transition temperature of the optical film may refer the glasstransition temperature of any layer of the optical film. For example,the glass transition temperature of the optical film may be the highestglass transition temperature of any of the layers of the optical film,may be the lowest glass transition temperature of any of the layers ofthe optical film, may be the glass transition temperature of thebirefringent interference layers of the optical film when the opticalfilm includes alternating nonbirefringent and birefringent layers, ormay be the glass transition temperature of the higher refractive indexinterference layers of the optical film 300 when the optical film 300includes alternating higher and lower index interference layers. Theglass transition temperature can be determined by differential scanningcalorimetry.

In some embodiments, prior to shaping the optical film, the optical filmis heated to a temperature that is below a melting temperature of theoptical film. The melting temperature may refer to the meltingtemperature of any of the layers of the optical film. In someembodiments, the melting temperature is the melting temperature of thehigher refractive index layer or of the birefringent layers. In someembodiments, prior to shaping the optical film, the optical film isheated to a temperature greater than a largest glass transitiontemperature of the optical film and lower than a lowest meltingtemperature of the optical film.

In some embodiments, the optical film 100 (or 100 b) is a reflectivepolarizer having a block axis substantially along the first direction.The block axis may be described as substantially along the firstdirection if an angle between the first direction and the block axis isless than 30 degrees. In some embodiments, the angle between the firstdirection and the block axis is less than 20 degrees, or less than 10degrees, or less than 5 degrees.

In some embodiments, the optical film 100 is a reflective polarizer andthe process includes stretching the reflective polarizer along the firstdirection 50 prior to shaping the optical film using the mold 250. Thishas been found to decrease the block state leakage of the reflectivepolarizer and increase the contrast ratio of the reflective polarizer.In some cases, buckling is introduced in the optical film by thisstretching but this buckling is subsequently remover during forming bypositioning the first and second rollers 20 and 25 sufficiently close tothe mold 250.

In some embodiments, the method further comprises disposing the opticalfilm adjacent third and fourth rollers. In some embodiments, shaping ofthe optical film includes moving the third and fourth rollers along thefirst direction. In some embodiments, the third roller is disposed toincrease a contact angle of the optical film with the first roller. Insome embodiments, the fourth roller is disposed to increase a contactangle of the optical film with the second roller. In some embodiments, aseparation between first and third rollers varies by no more than 10%during the shaping step, and a separation between second and fourthrollers varies by no more than 10% during the shaping step. For example,in some embodiments, the first and third rollers are disposed on acommon linear stage and so move together during the shaping of theoptical film. Similarly, in some embodiments, the second and fourthrollers are disposed on a common linear stage and so move togetherduring the shaping of the optical film. In other embodiments, each ofthe first, second, third and fourth rollers may be disposed on anindependent stage so that the separation distances can be independentlycontrolled. In some embodiments, the third roller is closer to the firstroller than to the second roller, and the fourth roller is closer to thesecond roller than to the first roller. FIGS. 2-3 illustrate twoembodiments where third and fourth rollers are included.

FIG. 2 is a schematic cross-sectional view illustrating a time in theshaping process where a mold 350 has initially contacted an optical film200. Optical film 200 is disposed adjacent first and second rollers 111and 112 and adjacent third 123 and fourth rollers 124 where the thirdroller 123 is proximate to the first roller 111 opposite the secondroller 112 and the fourth roller 124 is proximate the second roller 112opposite the first roller 111. The time in the shaping processillustrated in FIG. 2 is in many ways similar to the time in the shapingprocess of FIGS. 1A-1E illustrated in FIG. 1D except that third andfourth rollers 123 and 124 are included and the first and secondgripping means 130 and 135 are schematically illustrated as rollers. Theshaping method proceeds as illustrated and described for the shapingprocess of FIGS. 1A-1E. The separation d between the first and secondrollers 111 and 112 is typically varied to keep the threshold distancesd1 and d2 (see FIGS. 1D-1E) in a desired range as described furtherelsewhere herein. The third roller 123 is disposed to increase a contactangle θ of the optical film 200 with the first roller 111. Similarly,the fourth roller 124 is disposed to increase a contact angle of theoptical film 200 with the second roller 112. Increasing the contactangle with the first and second rollers 111 and 112 has been found toreduce any slipping of the optical film 200 along the rollers in thesecond direction and this has been found to further reduce any bucklingof the optical film 200.

In some embodiments, the first and second rollers 111 and 112 are heatedprior to and/or during the shaping of the optical film 200. In someembodiments, the third and fourth rollers 123 and 124 are also heated.In some embodiments, the first and second rollers 111 and 112 are eachat a higher temperature than each of the third and fourth rollers 123and 124 during the shaping step.

FIG. 3 is a schematic cross-sectional view illustrating a time in theshaping process where a mold 450 has initially contacted an optical film400. The optical film 300 is disposed adjacent first and second rollers211 and 212 and adjacent third and fourth rollers 223 and 224. The thirdroller 223 is proximate the first roller 211 and the fourth roller 224is proximate the second roller 212. The ends of the optical film 300 aredisposed in the first and second securing means 230 and 235 which may beor include clamps, grips or cylinders, for example. FIG. 3 may be asdescribed for FIG. 2 except for the positions of the third and fourthrollers 223 and 224 and the first and second securing means 230 and 235.The third roller 223 is disposed to increase a contact angle θ of theoptical film 300 with the first roller 211. Similarly, the fourth roller224 is disposed to increase a contact angle of the optical film 300 withthe second roller 212. The separation d between the first and secondrollers 111 and 112 is typically varied to keep the threshold distancesd1 and d2 (see FIGS. 1D-1E) in a desired range as described furtherelsewhere herein.

FIG. 4A is a schematic cross-sectional view of apparatus 1000 forprocessing optical film 400. The apparatus 1000 includes first andsecond rollers 420 and 425 spaced apart along a first direction(parallel to x-direction) and disposed on respective first and secondstages 421 and 426 configured to move the first and second rollers 420and 425 along the first direction. The first and second rollers 420 and425 have respective first and second widths (e.g., corresponding to WR1and WR2 depicted in FIG. 1B) along a second direction (parallel toy-direction) orthogonal to the first direction. The apparatus 1000further includes first and second securing means 430 and 435 forsecuring opposing first and second ends of the optical film 400; a mold1650 having a curved mold surface 1655 and disposed on a mold stage 1656configured to move the mold along a third direction (parallel toz-direction) orthogonal to the first and second directions; a means 1691for heating the optical film 400; a tension measuring means 1682 formeasuring a tension in the optical film; and a controller 1630. In theillustrated embodiment, the tension measuring means 1682 includes afirst tension measuring unit 1682 a and a second tension measuring unit1682 b. The first and second securing means 430 and 435 include thefirst and second tension measuring units 1682 a and 1682 b,respectively.

The first and second rollers 420 and 425 are disposed between the firstand second securing means 430 and 435. In some embodiments, theapparatus is configured such that when the first and second ends of theoptical film 400 are secured in the first and second securing means 430and 435, the optical film 400 contacts the first and second rollers 420and 425.

In some embodiments, the means 1691 for heating the optical film 400comprises a heater which may be or include one or more of an infraredheater, a convection heater, and a radiative heater. In someembodiments, means for heating the optical film further comprisesheating elements disposed in or on the mold 1650. In some embodiments,the means 1691 for heating the optical film 400 is disposed on a stage1696 configured to move the means 1691 along the second direction(parallel to y-direction). This can be done to move the means 1692farther from the optical film 400 near the end of the process so thatthe optical film 400 can cool. In some embodiments, a lens mount 1693 isdisposed on the stage 1696 as schematically illustrated in FIG. 4B. Thiscan be done to attach (e.g., bond using an optically clear adhesive) anoptical lens to the shaped film while it is still in contact with themold 1650 as described further elsewhere herein.

The controller 1630 is communicatively coupled to the tension measuringmeans 1682, the first and second stages 421 and 426, the first andsecond securing means 430 and 435, and the mold stage 1656. Thecommunicative coupling can be wired or wireless. In some embodiments,the controller is configured to simultaneously move the mold along thethird direction and move the first and second roller along the firstdirection while controlling the tension in the optical film 400.

In the illustrated embodiment, the first and second securing means 430and 435 comprise respective third and fourth stages 431 and 436.Alternatively, the first and second securing means 430 and 435 may bedescribed as being securing grips, clamps, or rollers, which aredisposed on respective separate stages that are communicatively coupledto the controller 1630. In some embodiments, the third and fourth stages431 and 436 are configured to move along the first direction. In someembodiments, the third and fourth stages 431 and 436 are communicativelycoupled to the controller 1630. In other embodiments, at least one ofthe first and second securing means 430 and 435 comprises a roller forsecuring the optical film 400 and includes a rotary stage to rotate theroller to control a tension in the film. In this case, the tensionmeasuring means may be or may include a torque meter attached to theroller.

FIGS. 5A-5B are side and perspective views of apparatus 5000 whichincludes first and second rollers 5020 and 5025 disposed on respectivefirst and second stages 5021 and 5026. The first and second stages 5021and 5026 include respective linear actuators 5022 and 5027 configured tomove the first and second rollers 5020 and 5025 along the firstdirection 550. The apparatus 5000 includes first and second securingmeans 5030 and 5035, which in the illustrated embodiment, includesecuring rollers. In other embodiments, securing grips or clamps may beused instead of securing rollers. The apparatus 5000 is configured suchthat when the first and second ends of an optical film are secured inthe first and second securing means 5030 and 5035, the optical filmcontacts the first and second rollers 5020 and 5025. The apparatus 5000includes a means 5091 for heating the optical film, which in theillustrated embodiment is an infrared heater. The apparatus 5000includes a tension measuring means for measuring a tension in theoptical film which includes first and second load cells 5082 a and 5082b. In the illustrated embodiment, the load cells 5082 a and 5082 b areS-type tension load cells. Other types of load cells may alternativelybe used. In some embodiments, the first and second securing means 5030and 5035 comprise respective third and fourth stages 5031 and 5036configured to move the first and second ends of the optical film alongthe first direction 550. In some embodiments, the third and fourthstages 5031 and 5036 are communicatively coupled to a controller. Forexample, the third and fourth stages 5031 and 5036 may include linearactuators wired to a controller. The apparatus 5000 includes a mold 5050having a curved mold surface and disposed on a mold mount 5051 whichattached to linear actuator 5056 through the actuator rod 5052. Thecombination of the mold mount 5051 and the linear actuator 5056including the actuator rod 5052 can be described as a mold stage. Thismold stage is configured to move the mold 5050 along a third direction5075. A frame (not shown for ease of illustration) is typically includedto support the linear actuator 5056 and other components.

In some embodiments, a method of shaping an optical film comprisescontacting the optical film with the curved mold surface whilestretching the optical film, resulting in a curved optical film curvedalong at least a first direction and in some cases along orthogonalfirst and second directions, where the stretching the optical filmduring the shaping step comprises stretching the optical film along thefirst direction greater than 3 times any stretching along the seconddirection. This can be accomplished using first and second rollers thatcan be moved to keep the threshold distances along the span of filmbetween the rollers and the mold in a desired range. This can also beaccomplished by applying a controlled first and second tension in theoptical film along first and second directions, respectively. In someembodiments, the optical film has first and second ends spaced apartalong the first direction, and has third and fourth ends spaced apartalong the second direction. The first and second ends may be secured infirst and second securing means configured to move the first and secondends along the first direction, and the third and fourth ends may besecured in third and fourth securing means configured to move along thesecond direction.

FIG. 6 is a schematic top view of a mold 650 disposed over an opticalfilm 600 which has a generally cross shape and includes a central region40 disposed between first and second ends and between third and fourthends. The first, second, third and fourth ends are secured in first,second, third and fourth securing means 630, 635, 633 and 637,respectively, which may be or include clamps, grips, or rollers asdescribed further elsewhere herein. The optical film 600 includes firstand second end regions extending 41 and 42 from the central region 40 tothe first and second ends, respectively; and includes third and fourthend regions 43 and 44 extending from the central region 40 to the thirdand fourth ends, respectively. In some embodiments, the first and secondend regions 41 and 42 have substantially constant first and secondwidths along a second direction 167 (parallel to y-direction) which maybe about equal. In some embodiments, the third and fourth end regions 43and 44 have substantially constant third and fourth widths along a firstdirection 150 (parallel to x-direction) which may be about equal. Insome embodiments, the first, second, third and fourth widths are aboutequal.

In some embodiments, the optical film 600 is disposed adjacent first,second, third and fourth rollers 620, 625, 653 and 654, respectively. Inother embodiments, the first, second, third and fourth rollers 620, 625,653 and 654 are omitted. The first and second rollers 620 and 625 may beconfigured to move along the first direction 150 and may be moved sothat the respective shortest distance between a point on the opticalfilm 600 contacting the respective roller and a point contacting acurved mold surface of the mold 650 is maintained in a preferred rangewhich may be any of the ranges described elsewhere herein for d1 and d2.Similarly, the third and fourth rollers 653 and 654 may be configured tomove along the second direction 167 and may be moved so that therespective shortest distance between a point on the optical film 600contacting the respective roller and a point contacting the curved moldsurface of the mold 650 is maintained in a preferred range which may beany of the ranges described elsewhere herein for d1 and d2.

The first and second rollers 620 and 625 may be replaced with pairs ofrollers as illustrated in FIGS. 2-3, for example. In this case, thethird and fourth rollers 653 and 654 may be referred to as fifth andsixth rollers. The third and fourth rollers 653 and 654 may also bereplaced with pairs of rollers as illustrated in FIGS. 2-3, for example.

In some embodiments, stretching the optical film 600 during the shapingstep comprises stretching the optical film along the first direction 150greater than 3 times, or greater than 5 times, or greater than 7 timesany stretching along the second direction 167. In some embodiments, theshaping step comprises changing positions of the first and second endsof the optical film 600 to control a first tension in the optical film600 along the first direction 150. In some embodiments, this is achievedby moving the first and second securing means 630 and 635 along thefirst direction 150. In other embodiments, at least one of the first andsecond securing means 630 and 635 comprises a roller for securing theoptical film 600 and includes a rotary stage to rotate the roller tocontrol the first tension. In some embodiments, the shaping stepcomprises changing positions of the third and fourth ends of the opticalfilm 600 to control a second tension in the optical film 600 along thesecond direction 167. In some embodiments, this is achieved by movingthe third and fourth securing means 633 and 637 along the seconddirection 167. In other embodiments, third and fourth securing means 633and 637 comprises a roller for securing the optical film 600 andincludes a rotary stage to rotate the roller to control the secondtension. In some embodiments, the first tension is greater than 2 times,or greater than 3 times, or greater than 5 times the second tension.

In some embodiments, the shaping step comprises changing positions ofthe third and fourth ends, which are in the third and fourth securingmeans 633 and 637, of the optical film 600 to reduce or eliminatebuckling of the optical film 600 in the second direction 167. In someembodiments, there is substantially no stretching of the optical film600 along the second direction 167. For example, a tension in the seconddirection 167 may be applied to keep the optical film 600 fromcontracting in the second direction 167, but the length of the film asmeasured along a curve in the second direction may not change, or maychange by less than 5%, during the shaping of the optical film 600.

In some embodiments, the optical film is pre-stretched along the firstdirection 150 more than the second direction 167 prior to shaping (e.g.,at least 2, or at least 3, or at least 5 times more). In someembodiments, the steps of securing, pre-stretching, and shaping arecarried out sequentially.

In some embodiments, an optical film is cut into a shape having acentral region and first through sixth end regions. This is useful forshaping the optical film into a shape having a substantially largerdiameter in a first direction than in an orthogonal second direction asillustrated in FIG. 7.

FIG. 7 is a schematic top view of a mold 750 disposed over an opticalfilm 700 including a central region 140 disposed between first andsecond ends, between third and fourth ends, and between fifth and sixthends. The first, second, third, fourth, fifth, and sixth ends aresecured in first, second, third, fourth, fifth and sixth securing means730, 735, 733, 737, 763, and 767, respectively, which may be grips orrollers as described further elsewhere herein. The optical film 700includes first and second end regions extending 141 and 142 from thecentral region 140 to the first and second ends, respectively; includesthird and fourth end regions 143 and 144 extending from the centralregion 40 to the third and fourth ends, respectively; and includes fifthand sixth end regions 165 and 166 extending from the central region 40to the third and fourth ends, respectively. In some embodiments, thefirst and second end regions 141 and 142 have substantially constantfirst and second widths along a second direction 267 (parallel toy-direction) which may be about equal. In some embodiments, the thirdand fourth end regions 143 and 144 have substantially constant third andfourth widths along a first direction 205 (parallel to x-direction)which may be about equal. In some embodiments, the fifth and sixth endregions 165 and 166 have substantially constant fifth and sixth widthsalong the first direction 205 which may be about equal. In someembodiments, the first, second, third, fourth, fifth, and sixth widthsare about equal.

In some embodiments, the optical film 700 is disposed adjacent first,second, third, four, fifth, and sixth rollers 720, 725, 753, 754, 775,and 776, respectively. In other embodiments, the first, second, third,fourth, fifth, and sixth rollers 720, 725, 753, 754, 775 and 776 areomitted. The first, second, third, and fourth rollers 720, 725, 753 and754 may be configured to move (along the first direction 205 for thefirst and second rollers 720 and 725, and along the second direction 267for the third and fourth rollers 753 and 754) to maintain the respectiveshortest distance between a point on the optical film 700 contacting therespective roller and a point contacting the curved mold surface of themold 750 as described for first, second, third, and fourth rollers 620,625, 653 and 654. Similarly, the fifth and sixth rollers 775 and 776 maybe configured to move along the second direction 267 and may be moved sothat the respective shortest distance between a point on the opticalfilm 700 contacting the respective roller and a point contacting thecurved mold surface of the mold 750 is maintained in a preferred rangewhich may be any of the ranges described elsewhere herein for d1 and d2.

The optical film 600 or the optical film 700 may be heated prior to (andoptionally during) the shaping step as described for optical film 100.The mold and rollers may also be heated prior to and optionally duringthe shaping step.

The methods of FIGS. 6-7 can also be used to alter a thicknessdistribution of the optical film 600 or 700 without shaping the opticalfilm into a curved shape. This can be done by suitably selecting thetensions in the first and second directions when the optical film isstretched.

FIG. 8A is a schematic top view of a portion 873 of an optical filmexhibiting buckling. Buckles 888 are illustrated. A cross-sectional viewthrough buckles 888 b in an optical film is schematically illustrated inFIG. 8B. Buckles 888 b may correspond to buckles 888. The bucklingexhibited in FIGS. 8A-8B is along the y-direction. Buckles arecharacterized by a curvature changing sign. Buckles 888 b have positiveand negative curvature regions in the cross-section of FIG. 8B withpoints where the curvature changes sign. The portion 873 may be anyportion of the optical film between first and second rollers spacedapart along the x-direction (e.g., first and second rollers 20 and 25),may be any portion of the optical film between third and fourth rollersspaced apart along the y-direction (e.g., third and fourth rollers 653and 654), or may be any portion of the optical film that has or willmake contact with a curved mold surface during the shaping of theoptical film. When a buckled film is formed onto the mold, there can beregions of negative Gaussian curvature where a local saddle shaperesults from buckling along one direction while being curve along anorthogonal direction. In this case, there are locations where theGaussian curvature changes sign. In some embodiments, the methods of thepresent description result in a shaped optical film having a Gaussiancurvature that is non-negative throughout the shaped optical film. Insome embodiments, the Gaussian curvature is positive throughout theshaped optical film.

Reducing the amplitude of the oscillations shown in FIG. 8B and/orreducing the number of buckles 888 b can be described as reducing thebuckling in the optical film. In some embodiments, the methods describedherein reduce or eliminate buckling of the optical film.

FIG. 8C is a schematic front plan view of an optical film 555illustrating a predetermined region 1010. Optical film 555 maycorrespond to any of the optical films of the present description (e.g.,optical film 100, optical film 100 b, optical film 200, optical film300, optical film 400) before the predetermined region 1010 is removedfrom remaining portions 1012 the optical film. Optical film 555 can beunderstood to have been shaped but the curvature is not shown in theschematic front plan view of FIG. 8C. In some embodiments, after shapingthe optical film 555, portions 1012 of the optical film 555 outside apredetermined region 1010 of the optical film 555 are removed (e.g., bycutting). The predetermined region 1010 may correspond to a majorsurface of an optical lens, for example. In some embodiments, the shapedoptical film has no points in the predetermined region 1010 where acurvature changes sign. In some embodiments, the shaped optical film hasno buckling in the predetermined region 1010. In some embodiments, themethods of the present description include the step of removing portions1012 so that the resulting shaped optical film corresponds to thepredetermined region 1010. In some embodiments, the optical film duringand after shaping but before removing portions 1012, the optical filmhas no buckling except for possibly along longitudinal edges 571 and/or572 outside of the predetermined region 1010. In some embodiments, theoptical film has buckling along longitudinal edges 571 and/or 572 duringthe shaping step which is subsequently removed due to thermally inducedshrinkage of the optical film along the longitudinal edges 571 and/or572.

Optical films may be described as having some specified variation alonga first direction and some specified variation along an orthogonalsecond direction. The first and second directions can be any orthogonaldirections relative to the optical film where the specified variationshold. In some cases, it may be desired to specify specific first andsecond directions as described further elsewhere herein. The first andsecond directions used to describe the optical film may or may notcorrespond to the first and second directions referred to in describingthe methods of shaping the optical film. The maximum sag of the opticalfilm along the first direction can be described as the maximumdisplacement of the optical film along a third direction orthogonal tothe first and second directions in a plane containing the first andthird direction. Similarly, the maximum sag of the optical film alongthe second direction can be described as the maximum displacement of theoptical film along the third direction in a plane containing the secondand third directions. This is schematically illustrated in FIGS. 9A-9B.The first, second, and third directions are the x′, y′, and z′directions, respectively. The optical film 900 has a first maximum sagS1 and a corresponding first diameter D1 along the first direction, andhas a second maximum sag S2 and a corresponding second diameter D2 alongthe second direction.

In some embodiments a first ratio, S1/D1, of the first maximum sag S1 tothe corresponding first diameter D1 along the first direction is atleast 0.05, or at least 0.1, or at least 0.15, or at least 0.2, or atleast 0.3, or at least 0.4, or at least 0.5, or at least 0.7. In someembodiments, the first ratio is less than 1, or less than 0.9, or lessthan 0.8. In some embodiments a second ratio, S2/D2, of the secondmaximum sag S2 to the corresponding second diameter D2 along the seconddirection is at least 0.05, or at least 0.1, or at least 0.15, or atleast 0.2, or at least 0.3, or at least 0.4. In some embodiments, thesecond ratio is less than 0.8, or less than 0.7, or less than 0.6, orless than 0.5. In some embodiments, the second ratio is less than thefirst ratio. In some embodiments, the first ratio is substantiallylarger (e.g., a factor of 1.5, or a factor of 2 larger) than the secondratio. In some embodiments, the second ratio is about equal to the firstratio.

FIG. 10A-10C are schematic perspective views of optical film 3000. Areference plane 3100 is defined such that the optical film 3000 has amaximum projected area 3110 in the reference plane 3100, the opticalfilm 3000 and the reference plane 3100 do not intersect, and at least amajority (e.g., at least 60%, or at least 80%, or all) of the total areaof the optical film 3000 is concave toward the reference plane 3100. Theoptical film 3000 has an apex 1015 which is the farthest point on theoptical film 3000 from the reference plane 3100. A projection 1075 ofthe apex 1015 onto the reference plane 3100 is illustrated. First andsecond directions 3150 and 3167 in the reference plane 3100 areillustrated. Each of the first and second directions 3150 and 3167 arein the reference plane 3100 and pass through the projection 1075 of theapex 1015 onto the reference plane 3100. First and second directions1016 and 1017 in a tangent plane at the apex 1015 are also illustrated.First direction 1016 may be parallel to first direction 3150, and seconddirection 1017 may be parallel to second direction 3167. Typically,properties of the optical film 3000 can be equivalently specified interms of first and second directions in the reference plane and in termsof first and second directions in the tangent plane.

In general, when the optical film 3000 has some specified variationsalong orthogonal first and second directions, the first and seconddirections 3150 and 3167 can be taken to be any orthogonal directionswhere optical film 3000 has the specified variations. In some cases, itis convenient to specifically define the first and second directions3150 and 3167 in terms of properties of the optical film 3000. There areat least two useful definitions of the first and second directions 3150and 3167.

In some embodiments, properties of the optical film 3000 (e.g., firstand second sag to diameter ratios described further elsewhere herein)are specified relative to first and second directions 3150 and 3167where the second direction 3167 is along a shortest distance betweenopposing sides 3201 and 3202 of the projected area 3110 through theprojection 1075 of the apex onto the reference plane 3100 and the firstdirection 3150 is along an orthogonal direction in the reference plane3100 through the projection 1075 of the apex 1015.

In some embodiments, the optical film 3000 is a reflective polarizer. Insome embodiments, properties of the reflective polarizer (e.g., firstand second sag to diameter ratios described further elsewhere herein)are specified relative to first and second directions 1016 and 1017where the first direction 1016 is along a block axis of the reflectivepolarizer at the apex 1015 and the second direction 1017 is along thepass axis of the reflective polarizer at the apex 1015.

Planes parallel to the reference plane 3100 that satisfy the conditionsthat the optical film and the plane do not intersect and that at least amajority of the total area of the optical film is concave toward theplane result in equivalent definitions of first and second directions.If there is more than one non-parallel plane having a same maximumprojected area and satisfying these conditions, then the first andsecond directions may be taken to be orthogonal directions where thespecified variations (e.g., sag ratios) hold and which are in a planeparallel to one of the planes having the maximum projected area. If oneof these planes results in apex closer to a center of the film alongeach of the first and second directions as defined relative to thatplane than the other planes having the maximum projected area, then thatplane may be used to define the first and second directions.

In some embodiments, properties of an optical film are specified forfirst and second curves or along the first and second curves. The firstcurve may be given as an intersection of the optical film with a firstplane orthogonal to the second direction and to the reference plane. Thefirst plane may contain the first direction and may contain an apex ofthe optical film. Similarly, the second curve may be an intersection ofthe optical film with a second plane orthogonal to the first directionand to the reference plane. The second plane may contain the seconddirection and may contain the apex of the optical film. Here, the firstand second directions may correspond to the first and second directions3150 and 3167 or may correspond to the first and second directions 1016and 1017.

FIG. 10B shows a first plane 3001 which is orthogonal to the seconddirection 3167 and to the reference plane 3100. In the illustratedembodiment, the first plane 3001 contains the first direction 3150 andthe apex 1015. A first curve 3010 being an intersection of the opticalfilm 3000 with the first plane 3001 is illustrated.

FIG. 10C shows a second plane 3002 which is orthogonal to the firstdirection 3150 and to the reference plane 3100. In the illustratedembodiment, the second plane 3002 contains the second direction 3167 andthe apex 1015. A second curve 3020 being an intersection of the opticalfilm 3000 with the second plane 3002 is illustrated. In someembodiments, the intersection of the first and second planes 3001 and3002 defines a line 3888 which is normal to the optical film 3000 at anintersection of the first and second curves 3010 and 3020.

In some cases, it is useful to characterize the shape of the opticalfilm in terms of Gaussian curvature and/or total curvature. The Gaussiancurvature is the product of the principle curvatures. For example, ifthe principle curvatures at the apex 1015 of the optical film 3000 occurin the first and second planes 3001 and 3002, the Gaussian curvature atthe apex can be expressed as the product of the curvatures at the apex1015 of the first and second curves 3010 and 3020. If, in addition, thefirst and second curved 3010 and 3020 have radii of curvature of r1 andr2 at the apex 1015, the Gaussian curvature at the apex can be expressedas 1/(r1*r2). In some embodiments, each location over at least 80%, orat least 90%, or at least 95% of the total area of the optical film hasa Gaussian curvature of at least 0.0001 cm⁻², or at least 0.001 cm⁻², orat least 0.005 cm⁻². In some embodiments, each location over at least80%, or at least 90%, or at least 95% of the total area of the opticalfilm has a Gaussian curvature of no more than 100 cm⁻², or no more than1 cm⁻², or no more than 0.2 cm⁻². The curvature of the optical film canalso be characterized in terms of the total curvature which is thesurface integral of the Gaussian curvature of the optical film over thetotal area of the optical film. In some embodiments, the optical filmhas a total curvature of at least 0.25, or at least 0.5, or at least 1,or at least 2, or at least 3. In some embodiments, the total curvatureis no more than 10, or no more than 9, or no more than 8.

FIG. 11A is a schematic illustration of a first curve 1110 and abest-fit first circular arc 1120. First curve 1110 may correspond tofirst curve 3010, for example. The best-fit first circular arc 1120subtends an angle α1 at the center of curvature 1177 of the firstcircular arc 1120. The angle α1 is determined by the first curve 1110since both a longer and a shorter circular arc would provide a poorerfit to the first curve 1110. The first circular arc 1120 has a radius R1which is a distance from any point on the best-fit first circular arc1120 (e.g., a first endpoint 1120 a) to the center of curvature 1177. Insome embodiments, the best-fit first circular arc 1120 is the circulararc that minimizes a sum of squared distances along normal vectors(e.g., distances along vectors 640 a-640 d) from the first circular arc1120 to points on the first curve 1110. In some embodiments, a firstendpoint 1110 a of first curve 1110 is along a first normal vector 640 ato the first circular arc 1120 at a first endpoint 1120 a of the firstcircular arc 1120, and an opposite second endpoint 1110 b of the firstcurve 1110 is along a second normal 640 d to the first circular arc 1120at an opposite second endpoint 1120 b of the first circular arc 1120. Insome embodiments, the points on the first curve 1110 used in thebest-fit minimization are selected from a predetermined set of pointsuniformly distributed over the first curve 1110. In some embodiments,the points on the first circular arc 1120 used in the minimization areselected from a predetermined set of points uniformly distributed overthe first circular arc 1120. In some embodiments, the predetermined setof points is a set of 10 to 500 points.

FIG. 11B is a schematic illustration of a second curve 1112 and abest-fit second circular arc 1122. Second curve 1112 may correspond tosecond curve 3020, for example. The best-fit circular arc subtends anangle α2 at the center of curvature 1178 of the second circular arc1122. The angle α2 is determined by the second curve 1112 since both alonger and a shorter circular arc would provide a poorer fit to thesecond curve 1112. The second circular arc 1122 has a radius R2 which isa distance from any point on the best-fit second circular arc 1122 tothe center of curvature 1178. The best fit can be determined asdescribed for the first curve 1110. In some embodiments, the best-fitsecond circular arc 1122 is the circular arc that minimizes a sum ofsquared distances along normal vectors (e.g., distances along vector641) from the second circular arc 1122 to points on the second curve1112. In some embodiments, a first endpoint of the second curve 1112 isalong a first normal vector to the second circular arc 1122 at a firstendpoint of the second circular arc 1122, and an opposite secondendpoint of the second curve 1112 is along a second normal to the secondcircular arc 1122 at an opposite second endpoint of the second circulararc 1122. In some embodiments, the points on the second curve 1112 usedin the best-fit minimization are selected from a predetermined set ofpoints uniformly distributed over the second curve 1112. In someembodiments, the points on the second circular arc 1122 used in theminimization are selected from a predetermined set of points uniformlydistributed over the second circular arc 1122. In some embodiments, thepredetermined set of points is a set of 10 to 500 points.

A center 1115 of the optical film and first and second location 1130 and1131 on the first curve 1110 are illustrated in FIG. 11A. The center1115 may be where the first and second curves 1110 and 1112 cross andmay be at an apex of the optical film as described further elsewhereherein. The second location 1131 is separated from the first location1130 by a distance along the first curve of at least 0.6 R1, or at least0.7 R1, or at least 0.8 R1, or at least R1, or at least 1.2 R1. Adistance from the center 1115 of the optical film to the first location1130 along the first curve is no more than 0.2 R1, or no more than 0.1R1. A distance from the second location 1131 to an edge of the opticalfilm (endpoint 1110 b) along the first curve 1110 is no more than 0.2R1, or no more than 0.1 R1. In some embodiments, the optical film has afirst thickness at the first location 1130 and a second thickness at thesecond location 1131, where the first and second thicknesses differ byno more than 5%, or no more than 3%, or no more than 2%. In someembodiments, the optical film has a first long wavelength band edge atthe first location 1130 and a second long wavelength band edge at thesecond location 1131, where the first and second long wavelength bandedges differ by no more than 5%, or no more than 3%, or no more than 2%.

FIG. 11C is a schematic plot of one possible thickness profile along thefirst curve 1110. FIG. 11G is a corresponding schematic plot of onepossible long wavelength band edge profile along the first curve 1110.The long wavelength band edge may be proportional to or approximatelyproportional to the thickness and so may have a same or similarly shapedprofile. The thickness (and/or long wavelength band edge) may be a localextremum (a local maximum, or a local minimum as shown in theillustrated embodiment) at the center 1115. The thickness (and/or longwavelength band edge) at the first location 1130 may be about equal tothe thickness (and/or long wavelength band edge) at the second location1131. The thickness (and/or long wavelength band edge) may varynon-monotonically from the first location 1130 to the second location1131. Another possible thickness variation along the first curve 1110 isschematically illustrated in FIG. 11D and a corresponding possible longwavelength band edge variation along the first curve 1110 isschematically illustrated in FIG. 11G. In this case, the thickness(and/or long wavelength band edge) decreases non-monotonically from thecenter 1115 to the endpoints 1110 a and 1110 b along the first curve1110. A possible thickness variation along the second curve 1112 isillustrated in FIG. 11E and a corresponding possible long wavelengthvariation along the second curve 1112 is illustrated in FIG. 11H. Inthis case, the thickness (and/or long wavelength band edge) increasesnon-monotonically from the center 1115 to endpoints along the secondcurve 1112. The thickness (and/or long wavelength band edge)distribution can be determined by applying the appropriate tension alongthe first direction in the forming of the optical film. The distributionmay be non-monotonic or monotonic (see, e.g., FIGS. 15A-15D) from thecenter of the optical film. In some cases, it has been found that asmaller overall thickness variation (and/or smaller overall longwavelength band edge variation) can be achieved if the thickness (and/orlong wavelength band edge) is allowed to vary non-monotonically in atleast one direction. In some embodiments, a maximum thickness variation((maximum thickness−minimum thickness)/maximum thickness) of the opticalfilm is less than 12%, or less than 10%, or less than 8%, or less than6%, or less than 5%, or less than 4%. In some embodiments, a maximumlong wavelength band edge variation of the optical film is less than12%, or less than 10%, or less than 8%, or less than 6%, or less than5%, or less than 4%.

The largest angles α1 and α2 achievable by the methods of the presentdescription are higher than those achievable in conventionalthermoforming methods. For example, in some embodiments, α1 is greaterthan 180 degrees, or greater than 185 degrees, or greater than 190degrees, or greater than 195 degrees, or greater than 200 degrees. Suchlarge angles may be useful in head-mounted display applications, forexample. In other embodiments, α1 is less than or equal to 180 degrees.In some embodiments, α1 is at least 90 degrees, or at least 100 degrees,or at least 110 degrees, or at least 120 degrees, or at least 130degrees, or at least 140 degrees, or at least 150 degrees, or at least160 degrees, or at least 170 degrees, or at least 180 degrees. In someembodiments, α2 is at least 30 degrees, or at least 40 degrees, or atleast 50 degrees, or at least 60 degrees, or at least 70 degrees, or atleast 80 degrees, or at least 90 degrees, or at least 100 degrees, or atleast 110 degrees, or at least 120 degrees. In some embodiments, α1 isno more than 350 degrees, or no more than 320 degrees, or no more than300 degrees, or no more than 280 degrees. In some embodiments, α2 is nomore than 220 degrees, or no more than 200 degrees, or no more than 180degrees, or no more than 160 degrees, or no more than 140 degrees. Insome embodiments, α1 is greater than or equal to α2.

FIG. 12 is a schematic side-view of a mold 1250 that can be used toshape an optical film to a subtended angle (e.g., α1 and optionally α2)greater than 180 degrees. Mold 1250 includes curved mold surface 1255which, in in the illustrated embodiment, is greater than half of asurface of a sphere. Mold 1250 includes a portion 1256 for mounting to amold actuator. In some embodiments, an optical film is shaped using mold1250 and the optical film is sufficiently flexible and stretchable toallow it to be removed from the mold 1250 after shaping.

FIG. 13 is a schematic cross-sectional view an optical film 1300 in aplane containing a first curve 1310. In the illustrated embodiment, thefirst curve 1310 is a circular arc subtending an angle α greater than180 degrees. In other embodiments, the first curve 1310 may not becircular but may define a best-fit circular arc subtending an angle αgreater than 180 degrees. In some cases, the angle α can approach 360degrees (e.g., about 350 degrees). The arc angle along a second curve inan orthogonal direction may be less than or equal to the angle α.

FIG. 14 is a schematic front plan view of an optical film 1400. Firstand second curves 1410 and 1420 are illustrated. The first and secondcurves 1410 and 1420 intersect at a center location 1430. As usedherein, a center location is a location at least twice as far from aclosest edge of the optical film than from a center of the optical film,and an edge location is a location at least twice as far from the centerof the optical film as from a closest edge of the optical film. Thecenter can be understood to be the apex (farthest point from thereference plane) as described further elsewhere herein. In someembodiments, the first and second curves 1410 and 1420 intersect eachother at the apex 1415.

In some embodiments, the first and second curves 1410 and 1420 aredefined by the intersection of the optical film 1400 with respectivefirst and second planes orthogonal to each other and orthogonal to areference plane (e.g., the x-y plane) in which the optical film 1400 hasa maximum projected area. In some embodiments, the optical film has afirst thickness distribution along the first curve 1410 that issubstantially symmetric under reflection about the second plane and asecond thickness distribution along the second curve 1420 that issubstantially symmetric under reflection about the first plane, wherethe first and second thickness distributions are different. For example,the first thickness distribution may be as illustrated in FIG. 15A andthe second thickness distribution may be as illustrated in FIG. 15B. Athickness distribution along a curve may be described as substantiallysymmetric under reflection about a plane if the thickness at each pointover at least 70% of the length of the curve differs from thecorresponding thickness at the reflected point by no more than 20%. Insome embodiments, the thickness at each point over at least 80% of thelength of the curve differs from the corresponding thickness at thereflected point by no more than 15%. In some embodiments, the thicknessat each point over at least 90% of the length of the curve differs fromthe corresponding thickness at the reflected point by no more than 10%.

In some embodiments, the optical film has a first long wavelength bandedge distribution along the first curve 1410 that is substantiallysymmetric under reflection about the second plane and a second longwavelength band edge distribution along the second curve 1420 that issubstantially symmetric under reflection about the first plane, wherethe first and second long wavelength band edge distributions aredifferent. For example, the first long wavelength band edge distributionmay be as illustrated in FIG. 15C and the second long wavelength bandedge distribution may be as illustrated in FIG. 15D. A long wavelengthband edge distribution along a curve may be described as substantiallysymmetric under reflection about a plane if the long wavelength bandedge at each point over at least 70% of the length of the curve differsfrom the corresponding long wavelength band edge at the reflected pointby no more than 20%. In some embodiments, the long wavelength band edgeat each point over at least 80% of the length of the curve differs fromthe long wavelength band edge at the reflected point by no more than15%. In some embodiments, the long wavelength band edge at each pointover at least 90% of the length of the curve differs from thecorresponding long wavelength band edge at the reflected point by nomore than 10%.

In some embodiments, the optical film 1400 has a thickness thatdecreases from the center location 1430 to a first edge location 1431 ofthe optical film 1400 along the first curve 1410 and increases from thecenter location 1430 to a second edge location 1432 along the secondcurve. In some embodiments, the thickness decreases non-monotonicallyfrom the center location 1430 to the first edge location 1431 along thefirst curve 1410. In some embodiments, the thickness decreasessubstantially monotonically from the center location 1430 to the firstedge location 1430 along the first curve 1410. In some embodiments, thethickness increases non-monotonically from the center location 1430 tothe second edge location 1432 along the second curve 1420. In someembodiments, the thickness increases substantially monotonically fromthe center location 1430 to the second edge location 1432 along thesecond curve 1420. In some embodiments, the thickness decreases (e.g.,non-monotonically or substantially monotonically) from the centerlocation 1430 to the third edge location 1433 along the first curve 1410opposite the first edge location 1431. In some embodiments, thethickness increases (e.g., non-monotonically or substantiallymonotonically) from the center location 1430 to the fourth edge location1434 along the second curve 1420 opposite the second edge location 1432.In some embodiments, the thickness at the center location 1430 is atleast 1%, or at least 2%, or at least 3%, or at least 4%, or at least 5%greater than the thickness at the first edge location 1431. In someembodiments, the thickness at the center location 1430 is at least 1%,or at least 2%, or at least 3%, or at least 4%, or at least 5% greaterthan the thickness at the third edge location 1433. In some embodiments,the thickness at the second edge location 1432 is at least 1%, or 2%, or3%, or at least 4%, or at least 5% greater than the thickness at thecenter location 1430. In some embodiments, the thickness at the fourthedge location 1434 is at least 1%, or 2%, or 3%, or at least 4%, or atleast 5% greater than the thickness at the center location 1430.

FIGS. 15A-15B are schematic illustrations of first and second thicknessdistributions 333 and 335 along respective first and second curves.FIGS. 15C-15D are schematic illustrations of first and second longwavelength band edge distributions 334 and 336 along respective firstand second curves. The first and second curves may be defined by theintersection of the optical film with first and second planes asdescribed further elsewhere herein. In some embodiments, the firstthickness distribution 333 is substantially symmetric under reflectionabout the second plane and the second thickness distribution 335 issubstantially symmetric under reflection about the first plane. Thefirst and second thickness distributions 333 and 335 are different. Thefirst thickness distribution 333 comprises a thickness that decreasesfrom a center location to each of opposing edge locations along thefirst curve. The second thickness distribution 335 comprises a thicknessthat increases from the center location to each of opposing edgelocations along the second curve. In the illustrated embodiment, thethickness decreases monotonically from a center location to each ofopposing edge locations along the first curve and increasesmonotonically from the center location to each of opposing edgelocations along the second curve. In other embodiments, the thicknessvariation may be non-monotonic along either of the first and secondcurves.

In some embodiments, the first long wavelength band edge distribution334 is substantially symmetric under reflection about the second planeand the second long wavelength band edge distribution 336 issubstantially symmetric under reflection about the first plane. Thefirst and second long wavelength band edge distributions 334 and 336 aredifferent. The first long wavelength band edge distribution 334comprises a long wavelength band edge that decreases from a centerlocation to each of opposing edge locations along the first curve. Thesecond long wavelength band edge distribution 336 comprises a longwavelength band edge that increases from the center location to each ofopposing edge locations along the second curve. In the illustratedembodiment, the long wavelength band edge decreases monotonically from acenter location to each of opposing edge locations along the first curveand increases monotonically from the center location to each of opposingedge locations along the second curve. In other embodiments, the longwavelength band edge variation may be non-monotonic along either of thefirst and second curves. The first and second long wavelength band edgedistributions 334 and 336 may be proportional to the first and secondthickness distributions 333 and 335, respectively.

A quantity, such as a thickness or a long wavelength band edge of anoptical film, may be said to substantially monotonically decrease over arange from a first end point of the range (e.g., center location of anoptical film) to a second end point of the range (e.g., an edge locationof the optical film) if the quantity at any larger intermediate point inthe range is less than or about equal to the quantity at any smallerintermediate point in the range. Similarly, a quantity may be said tosubstantially monotonically increase over a range from a first end pointof the range to a second end point of the range if the quantity at anylarger intermediate point in the range is greater than or about equal tothe quantity at any smaller intermediate point in the range. For aquantity that varies with locations over a range (e.g., thickness or along wavelength band edge over a range of locations from a centerlocation to an edge location), the quantity at a point may be said to beabout equal to a value (e.g., the quantity at another point) if thequantity at the point equals the value or if the quantity at the pointis in a range of the value plus or minus 5% of the maximum minus theminimum of the quantity over the range.

Other methods of thermoforming an optical film into a generally domedshape give a thickness (or long wavelength band edge) that is eitherlarge at a center of the film and decreases towards an edge in alldirections, or that is small near the center and increases towards theedges in all directions. FIGS. 22A and 22B plot the thicknessdistribution in an optical film formed into a spherical cap subtendingan angle of 120 degrees and 180 degrees, respectively, in apressurization process and in a pulldown process. The angle θ in theseplots are the angular position relative to the center of the film. Theedges of the films have a θ of 60 degrees and 90 degrees in FIGS.22A-22B, respectively. The thickness is rotationally symmetric about anoptical axis through an apex of films in these cases. In determiningthese thickness profiles, the optical film was assumed to be isotropicand incompressible, the circumferential stretching was assumed to beconstant in the pulldown process, and the radial stretching was assumedto be constant in the pressurization process. The curves show theapproximate thickness profile expected for a pulldown thermoformingprocess where the film is stretched such that the circumferentialstretching, but not the radial stretching, is substantially constant;and for a pressurization process where the film is stretched such thatthe radial stretching, but not the circumferential stretching, issubstantially constant. Stretching here refers to 1 plus strain, sostretching is constant when the strain is constant. The pulldown processcan be implemented on a MAAC vacuum thermoforming machine (availablefrom MAAC Machinery Corporation (Carol Stream, Ill.)) as described inU.S. Prov. Pat. Appl. No. 62/577,474 filed Oct. 26, 2017 and titled“SHAPED OPTICAL FILMS AND METHODS OF SHAPING OPTICAL FILMS” and thepressurization process can be implemented on a Hy-Tech forming machine(available from Hy-Tech Forming Systems (USA), Inc. (Phoenix, Ariz.))described in U.S. Prov. Pat. Appl. No. 62/577,474. The thickness dropsto zero at the edge of the film with a 180-degree subtended angle forthe pulldown process indicating that that attempting to form a film to asubtended angle this large in the pulldown process would result in localyielding of the film. The methods of the present description allow for asubstantially smaller overall thickness variation (and/or substantiallysmaller overall long wavelength band edge variation) to be obtained whenthe film is shaped to a large subtended angle and/or allows thethickness to vary differently in different directions and/or to becontrolled to have a desired thickness distribution which may or may notbe substantially monotonic.

The optical films of the present description may be mirror films orreflective polarizers, for example. In some embodiments, each locationover at least 80%, or over 85%, or over at least 90%, or over at least95% of a total area of the shaped optical film has a reflectance greaterthan about 80% for normally incident light having a same predeterminedwavelength and a same first polarization state. A polarization state canbe characterized by the direction of the electric field vector which fornormally incident light defines an axis tangent to the optical film. Ifthe axis tangent to the optical film along the electric field ofnormally incident light at two different locations on the optical filmare in parallel planes that each intersect the optical film along acurve (so that neither plane is tangent to the optical film at therespective first and second locations), the polarization states can beconsidered to be the same. If the axis that is tangent to the opticalfilm and that is perpendicular to the electric field of normallyincident light at two different locations on the optical film are inparallel planes that each intersect the optical film along a curve, thepolarization states can also be considered to be the same. For example,referring again to FIG. 14, the first polarization state may be thestate at the center location 1430 where the electric field of normallyincident light is along an axis 1437 in the first plane (e.g., a planeparallel to the x-z plane which may correspond to first plane 3001)defining the first curve 1410 at the center location 1430. Thepolarization state for light normally incident at a different locationis the same first polarization state if the axis tangent to the opticalfilm and along the electric field of the normally incident light at thedifferent location is in a plane parallel to the first plane. Forexample, a normally incident light at location 1441 may have an electricfield along axis 1443 when incident at location 1441 and this axis is inplane 1453 which is parallel to the first plane. A same secondpolarization state for normally incident light can be defined at eachlocation as the polarization state orthogonal to the first polarizationstate. In some embodiments, the optical film is a mirror film and has areflectivity that is about the same for the first and secondpolarization states. In some embodiments, the optical film is areflective polarizer has a substantially higher reflectivity for thefirst polarization state than for the second polarization state.

In some embodiments, the optical film 1400 is a reflective polarizer. Insome embodiments, each location on the reflective polarizer has amaximum reflectance and a corresponding minimum transmittance fornormally incident light polarized along a block axis, and a maximumtransmittance for normally incident light polarized along an orthogonalpass axis. For example, axes 1455 b and 1455 p at location 1455 may beblock and pass axes, respectively. The normally incident light may havea predetermined wavelength (e.g., about 550 nm) or may have wavelengthsin a predetermined wavelength range (e.g., 450 nm to 650 nm, or 400 nmto 700 nm).

FIG. 16 is a schematic plot of the transmittance of a reflectivepolarizer for the pass and block states of the reflective polarizer forlight normally incident on the reflective polarizer. The average of thetransmittance over wavelengths is a maximum for normally incident lighthaving a pass polarization state (polarized along a pass axis) and theaverage of the transmittance over wavelengths is a minimum for normallyincident light having a block polarization state (polarized along ablock axis). The average of the transmittance over wavelengths in thepredetermined wavelength range from λ1 to λ2 is Tp in the pass state andTb in the block state. In some embodiments, λ1 is about 450 nm and λ2 isabout 650 nm. In some embodiments, λ1 is about 400 nm and λ2 is about700 nm. In some embodiments Tp is at greater than about 80%, or greaterthan about 85%, or greater than 88%. In some embodiments, Tb is no morethan about 10%, or no more than about 5%, or no more than about 2%, orno more than about 1%, or no more than about 0.5%, or no more than 0.2%,or no more than 0.15%, or no more than 0.1%, or no more than 0.05%, orno more than 0.04%, or no more than 0.03%. In some embodiments, Tpand/or Tb is in any of these ranges at each location on a shaped opticalfilm over at least 80%, or at least 85%, or at least 90%, or at least95% of a total area of the shaped optical film.

A contrast ratio at a location on the reflective polarizer may bedefined as Tp/Tb. In some embodiments, each location in a region of thereflective polarizer having an area of at least 80% of a total area ofthe reflective polarizer has a contrast ratio being the maximum averagetransmittance (Tp) divided by the minimum average transmittance (Tb) ofat least 500. In some embodiments, the region has an area of least 85%,or at least 90%, or at least 95% of the total area. The region may beall of the reflective polarizer except for small portions near an edge,for example. A region 1490 of optical film 1400 is illustrated in FIG.14. Region 1490 is all of the optical film 1400 except for a smallportion along the edge. In some embodiments, the region is the portionof the reflective polarizer that is utilized in an optical systemincluding the reflective polarizer. In some embodiments, the region isthe entire reflective polarizer. In some embodiments, the contrast ratioTp/Tb at each location in the region is at least 1000, or at least 1100,or at least 1200, or at least 1300, or at least 1500, or at least 1600,or at least 1700, or at least 1800, or at least 1900, or at least 2000.In some embodiments, the reflective polarizer has a maximum contrastratio of at least 2000 (i.e., at least one location on the reflectivepolarizer has a contrast ratio of at least 2000), or at least 2500.

Another contrast ratio at a location on the reflective polarizer may bedefined as the maximum transmittance at a predetermined wavelengthdivided by the minimum transmittance at the predetermined wavelength.The predetermined wavelength may be a wavelength in the predeterminedwavelength range from λ1 to λ2. For example, the predeterminedwavelength may be (λ1+λ2)/2. In some embodiments, the predeterminedwavelength is about 550 nm. The contrast ratio defined at apredetermined wavelength may satisfy any of the conditions above for thecontrast ratio defined in terms of Tp and Tb which are averages over apredetermined wavelength range. For example, in some embodiments, eachlocation over at least 80% of a total area of the reflective polarizerhas a contrast ratio being the maximum transmittance for normallyincident light at the predetermined wavelength divided by the minimumtransmittance for normally incident light at the predeterminedwavelength of at least 500.

In some embodiments, the reflective polarizer includes a plurality ofpolymeric interference layers. The contrast ratio of a reflectivepolarizer can be increased by including more interference layers in agiven range. This can be done by including more layers in a singlepacket of alternating polymeric layers in a given thickness range or byincluding more than one packet of alternating polymeric layers withoverlapping thickness ranges as described further elsewhere herein. Suchtechniques can be used to provide a low Tb (e.g., less than 0.2%). Themethods of the present description allow substantially more stretchingof the reflective polarizer along the block axis than along theorthogonal pass axis and this has been found to increase the contrastratio of the shaped reflective polarizer relative to the initialunshaped reflective polarizer. In some embodiments, the initial unshapedfilm has a first contrast ratio and the shaped reflective polarizer hasa second contrast ratio. In some embodiments, for each location over atleast 60%, or over at least 70%, or over at least 80%, or over at least90%, or over 100% of a total area over the reflective polarizer, thesecond contrast ratio is greater than the first contrast ratio, orgreater than 1.2 times the first contrast ratio, or greater than 1.5times the first contrast ratio, or greater than 2 times the firstcontrast ratio.

FIG. 17 is a schematic plot of the reflectance of a reflective polarizerfor the pass and block states of the reflective polarizer for lightnormally incident on the reflective polarizer. The average of thereflectance over wavelengths is a maximum for normally incident lighthaving the block polarization state, and the average of the reflectanceover wavelengths is a minimum for normally incident light having thepass polarization state. The average of the reflectance over wavelengthsin the predetermined wavelength range from λ1 to λ2 is Rp in the passstate and Rb in the block is state. In some embodiments Rb is greaterthan about 75%, or greater than about 80%, or greater than about 85%, orgreater than about 90%. In some embodiments, Rp is no more than about20%, or no more than about 15%, or no more than about 10%, or no morethan about 5%. In some embodiments, Rp and/or Rb is in any of theseranges at each location on a shaped optical film over at least 80%, orat least 85%, or at least 90%, or at least 95% of a total area of theshaped optical film.

A long wavelength band edge λ3 is illustrated in FIGS. 16-17 and a shortwavelength band edge λ0 is indicated in FIG. 17. Reflection bandstypically have both long and short wavelength band edges where thereflectance rapidly drops. In the illustrated embodiment, the shortwavelength band edge λ0 is less than λ1 and the long wavelength bandedge λ3 is greater than λ2. The band edges may be determined fornormally incident light with the reflective polarizer convex towards theincident light. In some embodiments, an optical film has a longwavelength band edge λ3 (and/or a short wavelength band edge λ0) thatvaries with location in a pattern that is proportional to the patternsdescribed elsewhere herein for the thickness variation. In any opticalfilm of the present description where a thickness variation isspecified, the optical film may have a long wavelength band edge havinga variation proportional to the thickness variation. In someembodiments, an optical film has a long wavelength band edge as afunction of position that is proportional the thickness variationdepicted in any of FIGS. 11C-11E or 15A-15B.

The precise wavelength of a band edge can be defined using severaldifferent criteria. The spatial variation patterns exhibited by the bandedge typically do not depend on the precise criteria used. Thewavelength of the band edge may be can be taken to be the wavelengthwhere the reflectance for normally incident light having the blockpolarization state drops to ½ Rb or the wavelength where thetransmittance for normally incident light having the block polarizationstate increases to 10%, for example. Except where indicated differently,the band edge can be understood to refer to the wavelength where thetransmittance for normally incident light having the block polarizationstate increases to 10%.

The reflectance and transmittance can be determined for light normallyincident on either side of the optical film. Typically, similar resultsare obtained for either measurement. The optical film may be shaped foruse in a particular application where light is incident on one side ofthe optical film. In this case, the specified reflectance andtransmittance is for light incident on this side. In cases where theshaped optical film could be used in either orientation, the specifiedreflectance and transmittance can be understood to be for light incidenton the side of the shaped optical film such that the shaped optical filmis convex toward the incident light.

FIG. 18A is a schematic cross-sectional view of an optical film 1200including a plurality of interference layers 1234 and a noninterferencelayer 1233. In some embodiments, the plurality of interference layersincludes alternating polymeric layers 1236 and 1237. In the illustratedembodiment, a single noninterference layer 1233 is included.Interference layers may be described as reflecting or transmitting lightprimarily by optical interference when the reflectance and transmittanceof the interference layers can be reasonably described by opticalinterference or reasonably accurately modeled as resulting from opticalinterference. Such interference layers are described in U.S. Pat. No.5,882,774 (Jonza et al.), and U.S. Pat. No. 6,609,795 (Weber et al.),for example. Adjacent pairs of interference layers having differingrefractive indices reflect light by optical interference when the pairhas a combined optical thickness (refractive index times physicalthickness) of ½ the wavelength of the light. Interference layerstypically have a physical thickness of less than about 200 nanometers.Noninterference layers have an optical thickness too large to contributeto the reflection of visible light via interference. Typically,noninterference layers have a physical thickness of at least 1micrometer. In some embodiments, more than one noninterference layer isincluded. In some embodiments, at least one noninterference layer(noninterference layer 1233 in the illustrated embodiment) is integrallyformed with the plurality of interference layers 1234 and does notreflect or transmit light primarily by optical interference.

In some embodiments, at least one of the interference layers issubstantially uniaxially oriented prior to forming the film into acurved shape. For example, each of the layers 1237 may be substantiallyuniaxially oriented. A reflective polarizer or a layer in a reflectivepolarizer is substantially uniaxially oriented if it is substantiallyoriented in one in-plane direction and substantially not oriented in theorthogonal in-plane direction and substantially not oriented in thethickness direction. Substantially uniaxially oriented reflectivepolarizers are available from 3M Company under the trade designationAdvanced Polarizing Film or APF. Other types of multilayer optical filmreflective polarizers (e.g., Dual Brightness Enhancement Film or DBEFavailable from 3M Company) may also be used. DBEF films are orientedsubstantially more in one in-plane direction than in the orthogonalin-plane direction and also exhibit orientation in the thicknessdirection. DBEF films are not substantially uniaxially oriented as“substantially uniaxially oriented” is used herein.

In some embodiments, the reflective polarizer prior to forming into acurved shape is substantially uniaxially oriented in that it has adegree of uniaxial character U of at least 0.7, or at least 0.8, or atleast 0.85, where U=(1/MDDR−1)/(TDDR^(1/2)−1) with MDDR defined as themachine direction draw ratio and TDDR defined as the transversedirection draw ratio. Such substantially uniaxially oriented multilayeroptical films are described in U.S. Pat. No. 2010/0254002 (Merrill etal.), which is hereby incorporated herein to the extent that it does notcontradict the present description and may include a plurality ofalternating first and second polymeric layers with the first polymericlayers having indices of refraction in a length direction (e.g.,x-direction) and a thickness direction (e.g., z-direction) that aresubstantially the same, but substantially different from an index ofrefraction in a width direction (e.g., y-direction). For example, theabsolute value of the difference in the refractive indices in the x- andz-directions may be less than 0.02 or less than 0.01, and the absolutevalue of the difference in the refractive indices in the x- andy-directions may be greater than 0.05, or greater than 0.10. Exceptwhere specified differently, refractive index refers to the refractiveindex at a wavelength of 550 nm. After forming into a curved shape, areflective polarizer may have at least one layer that is substantiallyuniaxially oriented at at least one location. In some embodiments, theat least one layer at the at least one location has a first refractiveindex in a first direction along the thickness of the layer, a secondrefractive index in a second direction orthogonal to the firstdirection, and a third refractive index in a third direction orthogonalto the first and second directions, an absolute value of a difference inthe first and third refractive indices being less than about 0.02, orless than about 0.01, and an absolute value of a difference in thesecond and third refractive indices being greater than about 0.05, orgreater than about 0.10. In some embodiments, after being formed into acurved shape, a reflective polarizer has at least one layer that issubstantially uniaxially oriented at a plurality of locations.

In some embodiments, the optical film includes two or more packets ofalternating polymeric interference layers to provide a high contrast.Such optical films are described further in U.S. Prov. Pat. Appl. No.62/467,712 (Haag et al.), filed Mar. 6, 2017 and hereby incorporatedherein by reference to the extent that it does not contradict thepresent description. In some embodiments, the optical film is areflective polarizer and includes a plurality of packets where eachpacket has a layer thickness versus layer number that is a substantiallycontinuous curve. FIG. 18B is a schematic cross-sectional view of anoptical film 1322 which includes first and second packets 1224-1 and1224-2 of interference layers separated by noninterference layer 1326 b.The optical film 1322 further includes outer noninterference layers 1326a and 1326 c. The first and second packets 1224-1 and 1224-2 may utilizeoverlapping thickness ranges to provide a reflective polarizer, forexample, with a high contrast ratio (ratio of pass state transmittanceto block state transmittance) or a mirror with a low leakage. FIG. 19illustrates a layer thickness versus layer number for an optical film(e.g., reflective polarizer) including two packets (Packet 1 and Packet2). In some embodiments, the thickness profiles substantially overlap(e.g., greater than 50 percent of a thickness range of Packet 1 overlapsgreater than 50 percent of a thickness range of Packet 2). In otherembodiments, there is little or no overlap in the thickness ranges.

In some embodiments, the optical film is a mirror film such as a visiblelight mirror or a near-infrared mirror. Suitable mirror films includeEnhanced Specular Reflector (ESR) film available from 3M Company (St.Paul, Minn.).

The optical film 1200 and/or the optical film 1322 may be integrallyformed. As used herein, a first element “integrally formed” with asecond element means that the first and second elements are manufacturedtogether rather than manufactured separately and then subsequentlyjoined. Integrally formed includes manufacturing a first elementfollowed by manufacturing the second element on the first element. Aoptical film including a plurality of layers is integrally formed if thelayers are manufactured together (e.g., combined as melt streams andthen cast onto a chill roll to form a cast film having each of thelayers, and then orienting the cast film) rather than manufacturedseparately and then subsequently joined. In some embodiments, thenoninterference layers 1326 a and 1326 c are integrally formed with thefirst and second packets 1224-1 and 1224-2 of interference layers andthe noninterference layer 1326 b.

An additional layer not integral with the integrally formed multilayeroptical film means that the additional layer is not integrally formedwith the multilayer optical film. For example, the additional layer maybe formed separately and then subsequently adhered (e.g., laminatedusing an optically clear adhesive) to the multilayer optical film. Insome embodiments, the additional layer is a liner which is releasablyattached to the optical film. In some embodiments, two liners areincluded. For example, in some embodiments, the noninterference layers1326 a and 1326 c may be release liners releasably bonded and conformingto the first and second packets 1224-1 and 1224-2. In this case, theoptical film 1322 may be referred to as an optical stack and the layersbetween the noninterference layers 1326 a and 1326 c may be referred toas an optical film. In some embodiments, the release liner(s) areremoved prior to the shaping of the optical film. In some embodiments,the releaser liner(s) are shaped with the optical film so that theresulting shaped optical stack includes liner(s) releasably bonded andconforming to the optical film.

A liner that is bonded to an optical film but that can be cleanlyremoved from the optical film without substantially damaging the opticalfilm may be described as releasably bonded to the optical film and maybe described as a release liner. In some embodiments, a liner that isreleasably bonded to an optical film can be removed from the opticalfilm with no visible damage to the optical film. A releasably bondedliner may include a substrate with an adhesive layer that bonds stronglyto the substrate but weakly to the optical film. For example, a linermay include a thin layer of low tack adhesive applied to a substratewith a surface treated to increase its bond to the adhesive. Othersuitable liners include those that electrostatically bond to the opticalfilm as described in U.S. Pat. No. 6,991,695 (Tait et al.), for example.One example of a suitable liner is OCPET NSA33T available from Sun AKaken Co, Ltd.

Materials suitable for the higher refractive index interference layer inoptical film 1200 or 1322, include, for example, polyethylenenaphthalate (PEN), copolymers containing PEN and polyesters (e.g.,polyethylene terephthalate (PET) or dibenzoic acid), glycol modifiedpolyethylene terephthalate. Materials suitable for the lower refractiveindex interference layers in optical film 1200 or 1322, include, forexample, copolyesters based on PEN, copolyesters based on PET,polycarbonate (PC), or blends of these three classes of materials. Toachieve high reflectivities with a desired number of layers, adjacentmicrolayers can exhibit a difference in refractive indices for lightpolarized along the block axis of at least 0.2, for example.

In some embodiments, optical film 1200 or 1322 is a mirror film thatsubstantially reflects normally incident light in a predeterminedwavelength range for each of two orthogonal polarization stated. In someembodiments, optical film 1200 or 1322 is a reflective polarizer whichsubstantially reflects normally incident light in a predeterminedwavelength range polarized along a block axis and which substantiallyreflects normally incident light in a predetermined wavelength rangepolarized along an orthogonal pass axis.

In some embodiments, the shaped optical film resulting from the processis bonded to an optical lens. This can be done as step in the method ofshaping the optical film. FIG. 20A is a schematic cross-sectional viewof a portion of an optical film 1800 that has been stretched and shapedto at least partially conform to a curved mold surface of a mold 1850.An optical lens 1890 is disposed adjacent to the optical film 1800opposite the mold 1850. In some embodiments, the optical lens 1890 isdisposed on a lens mount (e.g., lens mount 1693). In some embodiments,an adhesive is applied to the curved major surface 1892 of the opticallens 1890. In some embodiments, the lens mount and the mold 1850 canmove towards one another until the adhesive on the optical lens 1890contacts the optical film 1800 and bonds the optical film 1800 to theoptical lens 1890. The adhesive can be applied uniformly to the curvedmajor surface 1892 of the optical lens 1890 or the adhesive can beapplied as a drop near the center of the curved major surface 1892 whichthen flows into an adhesive layer wetting out the curved major surface1892 when the optical lens 1890 and the mold closely approach oneanother. The mold 1850 and any excess portion of the optical film 1800is subsequently removed to form lens assembly 1842. FIG. 20B is aschematic cross-sectional view of lens assembly 1842 which includesoptical lens 1890, an adhesive layer 1844 and optical film 1800 bondedto the optical lens 1890 through the adhesive layer 1844. The opticalfilm 1800 conforms to the curved major surface 1892 of the optical lens1890.

In some embodiments, an optical lens comprises the curved mold surface.FIG. 21A is a schematic illustration of lens mount 1950 configured tohold optical lens 1990 which can be used as a mold in forming opticalfilm 1900. For example, in some embodiments the mold (e.g., mold 250)used in a method of shaping an optical film described elsewhere hereinis replaced with lens mount 1950 and optical lens 1990. FIG. 21Aillustrates a portion of an optical film 1900 that has been stretchedand shaped to at least partially conform to a curved major surface 1992of the optical lens 1990. An adhesive can be applied to the curved majorsurface 1992 prior to shaping the optical film 1900 to bond the opticalfilm 1900 to the curved major surface. FIG. 21B is a schematiccross-sectional view of lens assembly 1942 which includes and opticallens 1990 and an optical film 1900 bonded and conforming to the curvedmajor surface 1992 of the optical lens 1990. Lens assembly 1942 can beobtained by removing the lens mount 1950 and any excess portions of theoptical film 1900.

Terms such as “substantially” and “about” will be understood in thecontext in which they are used and described in the present descriptionby one of ordinary skill in the art. If the use of “about” as applied toquantities expressing feature sizes, amounts, and physical properties isnot otherwise clear to one of ordinary skill in the art in the contextin which it is used and described in the present description, “about”will be understood to mean within 10 percent of the specified value. Aquantity given as about a specified value can be precisely the specifiedvalue. For example, if it is not otherwise clear to one of ordinaryskill in the art in the context in which it is used and described in thepresent description, a quantity having a value of about 1, means thatthe quantity has a value between 0.9 and 1.1, and that the value couldbe 1.

The following is a list of exemplary embodiments of the presentdescription.

Embodiment 1 is a method of shaping an optical film, the methodcomprising the steps of: disposing the optical film adjacent first andsecond rollers such that a first portion of the optical film contactsthe first roller and a second portion of the optical film contacts thesecond roller, the first and second rollers spaced apart along a firstdirection, the first portion of the optical film having a first widthalong a second direction orthogonal to the first direction;

securing opposing first and second ends of the optical film, the firstand second ends spaced apart along the first direction, the first andsecond portions disposed between the first and second ends;

providing a curved mold surface; and

shaping the optical film by contacting the optical film with the curvedmold surface while stretching the optical film along the firstdirection,

wherein the shaping step comprises keeping a threshold distance betweenclosest first and second points less than about the first width, thefirst point on the optical film contacting the first roller, the secondpoint on the optical film contacting the curved mold surface.

Embodiment 2 is the method of Embodiment 1, wherein the first pointmoves along the first direction as the optical film is shaped.

Embodiment 3 is the method of Embodiment 1, wherein the second pointmoves along the first direction as the optical film is shaped.

Embodiment 4 is the method of Embodiment 1, wherein keeping thethreshold distance between the closest first and second points less thanabout the first width comprises moving the first roller along the firstdirection.

Embodiment 5 is the method of Embodiment 1, wherein shaping the opticalfilm comprises changing a separation distance between a point on aboundary of the curved mold surface and the optical film along a thirddirection orthogonal to the first and second directions.

Embodiment 6 is the method of Embodiment 1, wherein keeping thethreshold distance between the closest first and second points less thanabout the first width comprises changing a separation distance betweenthe first and second rollers along the first direction.

Embodiment 7 is the method of Embodiment 6, wherein changing theseparation distance between the first and second rollers along the firstdirection reduces buckling of the optical film along the seconddirection.

Embodiment 8 is the method of Embodiment 1, wherein the shaping stepcomprises changing positions of the first and second ends of the opticalfilm to control a tension in the optical film along the first direction.

Embodiment 9 is the method of Embodiment 8, wherein the tension in theoptical film along the first direction is substantially constant as thefilm is stretched.

Embodiment 10 is the method of Embodiment 8, wherein the tension in theoptical film along the first direction gradually increases during thestretching of the optical film.

Embodiment 11 is the method of Embodiment 8, wherein the tension iscontrolled to produce a desired thickness variation in the optical film.

Embodiment 12 is the method of Embodiment 8, wherein the tension iscontrolled to produce a thickness of the optical film that issubstantially constant along the first direction.

Embodiment 13 is the method of Embodiment 1, wherein the shaping stepcomprises keeping the threshold distance between the first and secondpoints in a range of 0.001 to 1 times the first width.

Embodiment 14 is the method of Embodiment 1, wherein the second portionof the optical film has a second width along the second direction, andwherein the shaping step further comprises keeping a threshold distancebetween closest third and fourth points less than about the secondwidth, the fourth point on the optical film contacting the secondroller, the third point on the optical film contacting the curved moldsurface.

Embodiment 15 is the method of Embodiment 14, wherein the shaping stepcomprises changing a separation distance between the first and secondrollers such that the threshold distance between the closest first andsecond points remains in a range of 0.001 to 1 times the first width andthe threshold distance between the closest third and fourth pointsremains in a range of 0.001 to 1 times the second width.

Embodiment 16 is the method of Embodiment 1, further comprisingdisposing the optical film adjacent third and fourth rollers, the thirdroller adjacent the first roller, the fourth roller adjacent the secondroller.

Embodiment 17 is the method of Embodiment 16, wherein the shaping stepfurther comprises changing the separation distance between the third andfourth rollers along the first direction.

Embodiment 18 is the method of Embodiment 17, wherein a separationbetween first and third rollers varies by no more than 10% during theshaping step, and a separation between second and fourth rollers variesby no more than 10% during the shaping step.

Embodiment 19 is the method of Embodiment 16, wherein the first andsecond rollers are each at a higher temperature than each of the thirdand fourth rollers during the shaping step.

Embodiment 20 is the method of Embodiment 16, wherein the third rolleris disposed to increase a contact angle of the optical film with thefirst roller.

Embodiment 21 is the method of Embodiment 16, wherein the fourth rolleris disposed to increase a contact angle of the optical film with thesecond roller.

Embodiment 22 is the method of Embodiment 1, wherein the method resultsin a shaped optical film having a first ratio of a first maximum sag toa corresponding first diameter along the first direction, and a secondratio of a second maximum sag to a corresponding second diameter alongthe second direction, the first ratio being at least 0.05.

Embodiment 23 is the method of Embodiment 1, wherein the optical filmcomprises a plurality of alternating polymeric interference layersreflecting and transmitting light primarily by optical interference.

Embodiment 24 is the method of Embodiment 1, wherein the optical film isa mirror film.

Embodiment 25 is the method of Embodiment 1, wherein the optical film isa reflective polarizer, each location on the reflective polarizer havinga maximum reflectance greater than about 80% for normally incident lighthaving a predetermined wavelength and polarized along a block axis, anda maximum transmittance greater than about 80% for normally incidentlight having the predetermined wavelength and polarized along anorthogonal pass axis.

Embodiment 26 is the method of Embodiment 25, wherein prior to shapingthe optical film, the block axis is substantially along the firstdirection.

Embodiment 27 is the method of Embodiment 1, further comprising heatingthe optical film.

Embodiment 28 is the method of Embodiment 27, further comprising heatingthe optical film prior to stretching the optical film.

Embodiment 29 is the method of Embodiment 27 or 28, further comprisingheating the optical film during the stretching of the optical film.

Embodiment 30 is the method of Embodiment 27, wherein the optical filmis heated to a temperature greater than a glass transition temperatureof the optical film.

Embodiment 31 is the method of Embodiment 27, wherein the optical filmis heated to a temperature greater than a largest glass transitiontemperature of the optical film and lower than a lowest meltingtemperature of the optical film.

Embodiment 32 is the method of Embodiment 1, wherein the optical filmhas no buckles between the first and second rollers and along the seconddirection between and away from longitudinal edges of the optical filmduring the shaping step.

Embodiment 33 is the method of any one of Embodiments 1 to 32, whereinthe method results in a shaped optical film having a first maximum sagalong the first direction, and a second maximum sag along the seconddirection, the first maximum sag greater than or equal to the secondmaximum sag, the second maximum sag greater than zero, each locationover at least 80% of a total area of the shaped optical film having areflectance greater than about 80% for normally incident light having asame predetermined wavelength and a same first polarization state.

Embodiment 34 is the method of any one of Embodiments 1 to 33 resultingin a shaped optical film, wherein the shaped optical film is areflective polarizer, each location on the reflective polarizer having amaximum reflectance and a corresponding minimum transmittance fornormally incident light polarized along a block axis and having thepredetermined wavelength, and a maximum transmittance for normallyincident light polarized along an orthogonal pass axis and having thepredetermined wavelength, the first direction being along the block axisat the apex, the second direction being along the pass axis at the apex.

Embodiment 35 is the method of Embodiment 34, wherein each location overat least 80% of a total area of the reflective polarizer has a contrastratio being the maximum transmittance divided by the minimumtransmittance of at least 500.

Embodiment 36 is a method of shaping an optical film, the methodcomprising the steps of:

disposing the optical film adjacent first and second rollers such that afirst portion of the optical film contacts the first roller and a secondportion of the optical film contacts the second roller, the first andsecond rollers spaced apart along a first direction, the first portionof the optical film having a first width along a second directionorthogonal to the first direction;securing opposing first and second ends of the optical film, the firstand second ends spaced apart along the first direction, the first andsecond portions disposed between the first and second ends; providing acurved mold surface; andshaping the optical film by contacting the optical film with the curvedmold surface while stretching the optical film along the firstdirection,wherein the shaping step comprises changing a separation distancebetween the first and second rollers along the first direction to reducebuckling of the optical film between the first and second rollers andalong the second direction between and away from longitudinal edges ofthe optical film.

Embodiment 37 is the method of Embodiment 36 resulting in a shapedoptical film having no points where a curvature changes sign.

Embodiment 38 is the method of Embodiment 36, wherein the optical filmhas no buckles between the first and second rollers during the shapingstep.

Embodiment 39 is the method of Embodiment 36, wherein the shaping stepcomprises keeping a threshold distance between closest first and secondpoints less than about the first width, the first point on the opticalfilm contacting the first roller, the second point on the optical filmcontacting the curved mold surface.

Embodiment 40 is the method of Embodiment 36, wherein the shaping stepcomprises changing positions of the first and second ends of the opticalfilm to control a tension in the optical film along the first direction.

Embodiment 41 is the method of Embodiment 36, further characterized byany one of Embodiments 1 to 35.

Embodiment 42 is a method of shaping an optical film, the methodcomprising the steps of: securing opposing first and second ends of theoptical film, the first and second ends spaced apart along a firstdirection;

securing opposing third and fourth ends of the optical film, the thirdand fourth ends spaced apart along a second direction orthogonal to thefirst direction;

providing a curved mold surface; and

shaping the optical film by contacting the optical film with the curvedmold surface while stretching the optical film, resulting in a curvedoptical film curved along at least the first direction, whereinstretching the optical film during the shaping step comprises stretchingthe optical film along the first direction greater than 3 times anystretching along the second direction.

Embodiment 43 is the method of Embodiment 42, wherein prior to shapingthe optical film, the optical film is generally cross shaped andcomprises:

a central region disposed between the first and second ends and betweenthe third and fourth ends; first and second end regions extending fromthe central region to the first and second ends, respectively; and

third and fourth end regions extending from the central region to thethird and fourth ends, respectively.

Embodiment 44 is the method of Embodiment 42, further comprising heatingthe optical film.

Embodiment 45 is the method of any one of Embodiments 1 to 23 or 25 to44, wherein prior to shaping the optical film, the optical film has afirst contrast ratio for normally incident light in a predeterminedwavelength range, and after shaping the optical film, the optical filmhas a second contrast ratio for normally incident light in thepredetermined wavelength range, wherein for each location across atleast 80% of a total area of the optical film, the second contrast ratiois greater than the first contrast ratio, each of the first and secondcontrast ratios being a ratio of the maximum transmittance of theoptical film for a pass polarization state to the minimum transmittanceof the optical film for a block polarization state.

Embodiment 46 is a curved optical film comprising a plurality ofpolymeric layers shaped along orthogonal first and second directionssuch that:

-   -   a first curve being an intersection of the optical film with a        first plane orthogonal to the second direction and to a        reference plane has a best-fit first circular arc subtending a        first angle at a center of curvature of the first circular arc        of greater than 180 degrees, the optical film having a maximum        projected area in the reference plane; and    -   a second curve being an intersection of the optical film with a        second plane orthogonal to the first direction and to the        reference plane has a best-fit second circular arc subtending a        second angle at a center of curvature of the second circular arc        of at least 30 degrees,        wherein each location across at least 90% of a total area of the        optical film has a reflectance greater than about 80% and a        transmittance less than about 2% for normally incident light        having a same predetermined wavelength and a same first        polarization state.

Embodiment 47 is the optical film of Embodiment 46, wherein the firstangle is at least 185 degrees.

Embodiment 48 is the optical film of Embodiment 46, wherein the firstcurve passes through a center of the optical film, the optical film hasa first thickness at first location along the first curve and a secondthickness at a second location along the first curve, the secondlocation separated from the first location by a distance along the firstcurve of at least 0.7 times a radius of curvature R of the first curveat the center of the optical film, a distance from the center of theoptical film to the first location along the first curve being no morethan 0.2 R, a distance from the second location to an edge of theoptical film along the first curve being no more than 0.2 R, the firstand second thicknesses differing by no more than 5%.

Embodiment 49 is a curved optical film comprising a plurality ofpolymeric layers shaped along orthogonal first and second directionssuch that:

-   -   a first curve being an intersection of the optical film with a        first plane orthogonal to the second direction and to a        reference plane has a best-fit first circular arc subtending a        first angle at a center of curvature of the first circular arc        of at least 90 degrees, the optical film having a maximum        projected area in the reference plane; and    -   a second curve being an intersection of the optical film with a        second plane orthogonal to the first direction and to the        reference plane has a best-fit second circular arc subtending a        second angle at a center of curvature of the second circular arc        of at least 30 degrees,        wherein each location across at least 90% of a total area of the        optical film has a reflectance greater than about 80% and a        transmittance less than about 2% for normally incident light        having a same predetermined wavelength and a same first        polarization state, and        wherein the first curve passes through a center of the optical        film, the optical film has a first thickness at a first location        along the first curve and a second thickness at a second        location along the first curve, the second location separated        from the first location by a distance along the first curve of        at least 0.7 times a radius R1 of the best-fit first circular        arc, a distance from the center of the optical film to the first        location along the first curve being no more than 0.2 R1, a        distance from the second location to an edge of the optical film        along the first curve being no more than 0.2 R1, the first and        second thicknesses differing by no more than 5%.

Embodiment 50 is the optical film of any one of Embodiments 46 to 49,wherein the reference plane does not intersect the optical film, atleast a majority of the optical film is concave toward the referenceplane, an apex of the optical film has a maximum distance from thereference plane, and the first and second curves intersect at the apex.

Embodiment 51 is the optical film of any one of Embodiments 46 to 50,wherein the reference plane does not intersect the optical film, atleast majority of the optical film is concave toward the referenceplane, an apex of the optical film has a maximum distance from thereference plane, the second direction is along a shortest distancebetween opposing sides of the maximum projected area through aprojection of the apex onto the reference plane and the first directionis along an orthogonal direction in the reference plane through theprojection of the apex.

Embodiment 52 is the optical film of any one of Embodiments 46 to 51,wherein the best-fit first circular arc minimizes a sum of squareddistances along normal vectors from the first circular arc to points onthe first curve, a first endpoint of first curve being along a firstnormal vector to the first circular arc at a first endpoint of the firstcircular arc, an opposite second endpoint of the first curve being alonga second normal to the first circular arc at an opposite second endpointof the second circular arc.

Embodiment 53 is the optical film of Embodiment 52, wherein the pointson the first curve are selected from a predetermined set of pointsuniformly distributed over the first curve.

Embodiment 54 is the optical film of Embodiment 52, wherein the pointson the first circular arc are selected from a predetermined set ofpoints uniformly distributed over the first circular arc.

Embodiment 55 is the optical film of Embodiment 53 or 54, wherein thepredetermined set of points is a set of 10 to 500 points.

Embodiment 56 is a curved optical film comprising a plurality ofpolymeric layers shaped along orthogonal first and second directionssuch that:

-   -   a first curve being an intersection of the optical film with a        first plane orthogonal to the second direction and to a        reference plane has a best-fit first circular arc subtending a        first angle at a center of curvature of the first circular arc        of at least 90 degrees, the optical film having a maximum        projected area in the reference plane; and    -   a second curve being an intersection of the optical film with a        second plane orthogonal to the first direction and to the        reference plane has a best-fit second circular arc subtending a        second angle at a center of curvature of the second circular arc        of at least 30 degrees,        wherein each location across at least 90% of a total area of the        optical film has a reflectance greater than about 80% and a        transmittance less than about 2% for normally incident light        having a same predetermined wavelength and a same first        polarization state, and        wherein the first curve passes through a center of the optical        film, the optical film has a first long wavelength band edge at        a first location along the first curve and a second long        wavelength band edge at a second location along the first curve,        the second location separated from the first location by a        distance along the first curve of at least 0.7 times a radius R1        of the best-fit first circular arc, a distance from the center        of the optical film to the first location along the first curve        being no more than 0.2 R1, a distance from the second location        to an edge of the optical film along the first curve being no        more than 0.2 R1, the first and second long wavelength band        edges differing by no more than 5%.

Embodiment 57 is an optical film comprising a plurality of polymericlayers, each location across at least 90% of a total area of the opticalfilm having a reflectance greater than about 80% and a transmittanceless than about 5% for normally incident light having a samepredetermined wavelength and a same first polarization state, whereinfor orthogonal first and second planes intersecting the optical filmalong respective first and second curves, the first and second curvesintersecting each other at a center location of the optical film, theoptical film has a thickness that decreases from the center location toa first edge location of the optical film along the first curve andincreases from the center location to a second edge location along thesecond curve.

Embodiment 58 is the optical film of Embodiment 57, wherein anintersection of the first and second planes define a line normal to theoptical film at the center location.

Embodiment 59 is an optical film comprising a plurality of polymericlayers, each location across at least 90% of a total area of the opticalfilm having a reflectance greater than about 80% and a transmittanceless than about 5% for normally incident light having a samepredetermined wavelength and a same first polarization state, whereinfor orthogonal first and second planes intersecting the optical filmalong respective first and second curves, the first and second curvesintersecting each other at a center location of the optical film, theoptical film has a long wavelength band edge that decreases from thecenter location to a first edge location of the optical film along thefirst curve and increases from the center location to a second edgelocation along the second curve.

Embodiment 60 is the optical film of Embodiment 59, wherein anintersection of the first and second planes define a line normal to theoptical film at the center location.

Embodiment 61 is an optical film comprising a plurality of polymericlayers, each location across at least 90% of a total area of the opticalfilm having a reflectance greater than about 80% and a transmittanceless than about 5% for normally incident light having a samepredetermined wavelength and a same first polarization state, whereinfor orthogonal first and second planes intersecting the optical filmalong respective first and second curves, the optical film has a firstthickness distribution along the first curve that is substantiallysymmetric under reflection about the second plane and a second thicknessdistribution along the second curve that is substantially symmetricunder reflection about the first plane, the first and second thicknessdistributions being different.

Embodiment 62 is the optical film of any one of Embodiments 57 to 61,wherein the first curve has a best-fit first circular arc subtending afirst angle at a center of curvature of the first circular arc of atleast 90 degrees, and the second curve has a best-fit second circulararc subtending a second angle at a center of curvature of the secondcircular arc of at least 30 degrees.

Embodiment 63 is an optical film comprising a plurality of polymericlayers, each location across at least 90% of a total area of the opticalfilm having a reflectance greater than about 80% and a transmittanceless than about 5% for normally incident light having a samepredetermined wavelength and a same first polarization state, whereinfor orthogonal first and second planes intersecting the optical filmalong respective first and second curves, the optical film has a firstlong wavelength band edge distribution along the first curve that issubstantially symmetric under reflection about the second plane and asecond long wavelength band edge distribution along the second curvethat is substantially symmetric under reflection about the first plane,the first and second long wavelength band edge distributions beingdifferent.

Embodiment 64 is the optical film of Embodiment 63, wherein the firstand second curves intersect at a center location of the optical film andthe first long wavelength band edge distribution comprises a longwavelength band edge that decreases from the center location to a firstedge location of the optical film along the first curve.

Embodiment 65 is the optical film of Embodiment 64, wherein the secondlong wavelength band edge distribution comprises a long wavelength bandedge that increases from the center location to a second edge locationof the optical film along the second curve.

Embodiment 66 is the optical film of Embodiment 63, wherein the firstand second curves intersect at a center location of the optical film andthe first long wavelength band edge distribution comprises a longwavelength band edge that decreases from the center location to a firstedge location of the optical film along the first curve, and the secondlong wavelength band edge distribution comprises a long wavelength bandedge that increases from the center location to a second edge locationof the optical film along the second curve.

Embodiment 67 is a curved reflective polarizer comprising a plurality ofpolymeric layers shaped along at least orthogonal first and seconddirections so that a first ratio of a first maximum sag to acorresponding first diameter along the first direction is at least 0.1,and a second ratio of a second maximum sag to a corresponding seconddiameter along the second direction is at least 0.05, wherein fornormally incident light in a predetermined wavelength range, eachlocation on the reflective polarizer has a maximum average reflectancegreater than about 80% and a corresponding minimum average transmittanceless than about 2% for a block polarization state, and a maximum averagetransmittance greater than about 80% for an orthogonal pass polarizationstate, wherein each location in a region of the reflective polarizerhaving an area of at least 80% of a total area of the reflectivepolarizer has a contrast ratio being the maximum average transmittancedivided by the minimum average transmittance of at least 500.

Embodiment 68 is a curved reflective polarizer comprising a plurality ofpolymeric layers shaped along orthogonal first and second directionssuch that a total curvature of the reflective polarizer is at least0.25, the total curvature being a surface integral of a Gaussiancurvature of the reflective polarizer over a total area of thereflective polarizer, wherein for normally incident light in apredetermined wavelength range, each location on the reflectivepolarizer has a maximum average reflectance greater than about 80% and acorresponding minimum average transmittance less than about 2% for ablock polarization state, and a maximum average transmittance greaterthan about 80% for an orthogonal pass polarization state, wherein eachlocation in a region of the reflective polarizer having an area of atleast 80% of the total area of the reflective polarizer has a contrastratio being the maximum average transmittance divided by the minimumaverage transmittance of at least 500.

Embodiment 69 is the reflective polarizer of Embodiment 68, wherein afirst ratio of a first maximum sag to a corresponding first diameteralong the first direction is at least 0.1, and a second ratio of asecond maximum sag to a corresponding second diameter along the seconddirection is at least 0.05.

Embodiment 70 is the reflective polarizer of any one of Embodiments 67to 68, wherein for a predetermined wavelength in the predeterminedwavelength range, each location over at least 80% of the total area ofthe reflective polarizer has a transmittance less than about 0.2% fornormally incident light having the block polarization state.

Embodiment 71 is a curved reflective polarizer comprising a plurality ofpolymeric layers shaped along orthogonal first and second directionssuch that a total curvature of the reflective polarizer is at least0.25, the total curvature being a surface integral of a Gaussiancurvature of the reflective polarizer over a total area of thereflective polarizer, wherein for normally incident light having apredetermined wavelength, each location over at least 80% of a totalarea of the reflective polarizer has a maximum reflectance greater thanabout 80% and a corresponding minimum transmittance less than about 0.2%for a block polarization state, and a maximum transmittance greater thanabout 80% for an orthogonal pass polarization state.

Embodiment 72 is the reflective polarizer of Embodiment 71, wherein afirst ratio of a first maximum sag to a corresponding first diameteralong the first direction is at least about 0.1, and a second ratio of asecond maximum sag to a corresponding second diameter along the seconddirection is at least about 0.05.

Embodiment 73 is the reflective polarizer of Embodiment 71 or 72,wherein each location over at least 90% of a total area of thereflective polarizer has a minimum transmittance less than about 0.2%for the block polarization state.

Embodiment 74 is an apparatus for processing optical film, the apparatuscomprising:

first and second rollers spaced apart along a first direction anddisposed on respective first and second stages configured to move thefirst and second rollers along the first direction, the first and secondrollers having respective first and second widths along a seconddirection orthogonal to the first direction;

first and second securing means for securing opposing first and secondends of the optical film, the first and second rollers disposed betweenthe first and second securing means, the apparatus being configured suchthat when the first and second ends of the optical film are secured inthe first and second securing means, the optical film contacts the firstand second rollers;

a mold having a curved mold surface and disposed on a mold stageconfigured to move the mold along a third direction orthogonal to thefirst and second directions;

a means for heating the optical film;

a tension measuring means for measuring a tension in the optical film;

a controller communicatively coupled to the tension measuring means, thefirst and second stages, the first and second securing means, and themold stage, the controller being configured to simultaneously move themold along the third direction and move the first and second rolleralong the first direction while controlling the tension in the opticalfilm.

Embodiment 75 is the apparatus of Embodiment 74, wherein the controlleris adapted to control the tension by adjusting a distance along thefirst direction between the first and second securing means.

Embodiment 76 is the apparatus of Embodiment 74, wherein the first andsecond securing means comprise respective third and fourth stagesconfigured to move the first and second ends of the optical film alongthe first direction, the third and fourth stages being communicativelycoupled to the controller.

Embodiment 77 is the apparatus of any one of Embodiments 74 to 76,wherein each of the first and second securing means comprise a securingroller or securing grips.

Embodiment 78 is the apparatus of Embodiment 74, wherein the means forheating the optical film comprises a heater spaced apart from the moldalong the third direction.

Embodiment 79 is the apparatus of Embodiment 74, wherein the means forheating the optical film comprises heating elements disposed in or onthe mold.

Embodiment 80 is the apparatus of Embodiment 74 further comprising theoptical film, wherein a temperature of the optical film is lower at afirst point of the optical film contacting the curved mold surface thanat a second point of the optical film not contacting the curved moldsurface.

EXAMPLES

Reflective Polarizer 1

Two multilayer optical packets were co-extruded with each packetcomprised of 325 alternating layers of polyethylene naphthalate (PEN)and a low index isotropic layer, which was made with a blend ofpolycarbonate and copolyesters (PC:coPET) such that the index is about1.57 and remains substantially isotropic upon uniaxial orientation,wherein the PC:coPET molar ratio is approximately 42.5 mol % PC and 57.5mol % coPET and has a Tg of 105 degrees centigrade. This isotropicmaterial was chosen such that after stretching its refractive indices inthe two non-stretch directions remains substantially matched with thoseof the birefringent material in the non-stretching direction while inthe stretching direction there is a substantial mis-match in refractiveindices between birefringent and non-birefringent layers. The PEN andPC/coPET polymers were fed from separate extruders to a multilayercoextrusion feedblock, in which they were assembled into packets of 325alternating optical layers (“Packet 1” and “Packet 2” respectively),plus a thicker protective boundary layer of the PC/coPET, on the outsideof the stacked optical packets, for a total of 652 layers. The film wassubstantially uniaxially stretched in a parabolic tenter as described inU.S. Pat. No. 6,916,440 (Jackson et al.). The film was stretched at atemperature of about 150° C. to a draw ratio of about 6. The layerthickness profile for the resulting reflective polarizer is shown inFIG. 19 with Packets 1 and 2 indicated. Several samples were made havinga total thickness as measured by a capacitance gauge of approximately62-64 μm. Protective olefin liners were applied to each side of thereflective polarizer.

Example 1

Optical films were shaped using an apparatus similar to that illustratedin FIG. 2. A picture of the mold (corresponding to mold 350) is providedin FIG. 23A. The mold was a Base 8 form having a spherical radius ofcurvature of 65.3 mm, a diameter of 90 mm, a maximum angle subtended atthe center of curvature of 87.1 degrees, a contour length (length alonggeodesic through apex) of 99.3 mm, a sag of 17.9 mm, and a sag todiameter ratio of 0.199, and a total curvature of 1.72.

Samples were shaped using one of two processing conditions. Forcondition 1, an 80 mm by 1200 mm wide piece of Reflective Polarizer 1film was cut with the long direction aligned with the block direction ofthe film. The grips (corresponding to securing means 130 and 135) wereset to a distance of 680 mm apart, the inner rollers (corresponding tofirst and second rollers 111 and 112) were set a distance of 230 mmapart (measured from center to center), and the film was loaded into theapparatus with the film passing over the inside rollers and under theoutside rollers. The outer rollers centers were positioned 65 mm outsidethe inner rollers and traveled with inner rollers. The olefin linerswere then peeled from the film and threaded out through the rollers. Atension of about 35N was applied to the film. The film was heated to170° C. with a 600 W, 125 mm×125 mm Ceramic type IR heater (supplied byWECO International) located ˜150 mm below the film. The temperature wasmonitored using an IR temperature sensor with a 12 mm spot size. Whenthe film reached the set temperature, the tension was increased to about500N and the rollers were moved to a center-to-center separationdistance between the inner rollers of 105 mm. Once the rollers were inplace the mold was plunged into the film at a rate if 2 mm/sec until themold moved 45 mm after initially contacting the film. After 7.1 seconds,the rollers were moved outward to maintain a free-span length betweenthe point of contact on the mold and the point of contact on therespective roller of ˜15-20 mm as the mold continued its downward path.During this process, the film tension was monitored with two load cellsmounted on the grips and the grips were moved to maintain a constanttension of about 500 N. The IR heat was maintained on the film duringthis process. Once the mold and rollers reached their final positions,the part was held over the IR heater for another 113 seconds to helprelax any stresses in the film. The heater was then moved away and thefilm (and mold) were allowed to cool for 5 min in ambient air. Aftercooling, the film tension was removed and the rollers and mold movedapart to allow the shaped film to be removed from the machine.

For Condition 2, a sample of Reflective Polarizer 1 film was loaded intothe apparatus as described for Condition 1 and the olefin liners werethen peeled from the film and threaded out through the rollers. Atension of about 35N was applied to the film. The film was heated to170° C. as described for Condition 1. When the film reached the settemperature, the tension was increased to about 250N and the rollerswere moved to a center-to-center separation distance between the innerrollers of 105 mm. Once the rollers were in place the mold was plungedinto the film at a rate if 2 mm/sec until the mold moved 55 mm afterinitially contacting the film. After 6.7 seconds, the rollers were movedoutward to maintain a free-span length between the point of contact onthe mold and the point of contact on the respective roller of ˜10-15 mmas the mold continued its downward path. After another 15 seconds, thefilm tension was increased to about 350 N. After another 20 seconds, theseparation between the rollers was increased by an additional 30 mm andthe mold was plunged down another 17 mm. This was done to position thefilm closed to the heater. The film was held over the IR heater for anadditional 165 sec. The heater was then moved away and the film (andmold) were allowed to cool for 5 min in ambient air. After cooling, thefilm tension was removed and the rollers and mold moved apart to allowthe shaped film to be removed from the machine.

The reflective polarizer samples were mounted onto a goniometer fixtureand the samples were rotated to place the desired region of the samplein the light path with the test region surface normal to the beam. Thesample was oriented so that it was convex towards the incident beam.Samples were tested at center (C), north (N), northeast (NE), east (E),southeast (SE), south (S), southwest (SW), west (W), and northwest (NW)locations as schematically illustrated in FIG. 24 which is a top planview of reflective polarizer 2400. The block direction of the reflectivepolarizer was along the north-south direction at the center. The passstate transmission and the block state transmission was measured atnormal incidence as a function of wavelength using a Lambda 1050spectrophotometer (available from PerkinElmer, Waltham, Mass.). Theaverage block state transmission Tb and the average pass statetransmission Tp was determined over the wavelength range of 450 nm to650 nm and the corresponding contrast ratio Tp/Tb was determined. Thelong wavelength band edge was determined as the wavelength where theblock state transmission reached 10%. The average block statetransmission, the average pass state transmission, the contrast ratio,and the long wavelength band edge are shown in FIGS. 25-27,respectively, for Reflective Polarizer 1 samples shaped under conditions1 and 2 and for samples prior to shaping (preshaped). The results for aReflective Polarizer 1 film shaped in a pulldown process of a MAACsystem as described in U.S. Prov. Pat. Appl. No. 62/577,474 are shownfor comparison. The block state transmission was significantly lower forthe films shaped according to the present description compared to thepulldown process while the pass state transmission was higher and thecontrast ratio was substantially higher. For the sample shaped usingCondition 2, the contrast ratio was higher than the preshaped sampleover most of the reflective polarizer.

The average block and pass state transmission over the same wavelengthrange and the corresponding contrast ratio was also determined for asample shaped using Condition 2 at the points described above and theresults were linearly interpolated over an area of film to producecontour plots. Measurements were performed with the light normallyincident on the reflective polarizer and the reflective polarizeroriented such that it was convex towards the incident light. Positionswere described in terms of angles phi_x and phi_y where tan(phi_x)=X/Z,tan(phi_y)=Y/X, where X,Y,Z are orthogonal coordinates with an origin atthe center of curvature of the reflective polarizer, Z is along a normalto the reflective polarizer at the apex of the reflective polarizer, Yis along the block axis at the apex, and X is orthogonal to Y. Theresulting contour plots of the average block state transmission, theaverage pass state transmission and the contrast ratio are shown inFIGS. 29-31, respectively.

Example 2

Optical films were shaped using an apparatus similar to that illustratedin FIG. 2. A picture of the mold (corresponding to mold 350) is providedin FIG. 23B. The mold had a spherical radius of curvature of 50 mm, adiameter along a first (long) direction of 100 mm, a diameter along anorthogonal second direction of 50 mm, a maximum angle subtended at thecenter of curvature of 200 degrees along the first direction and 73.7degrees along the second direction, a contour length (length alonggeodesic through apex) along the first direction of 174.5 mm, a maximumsag of 58.7 mm and a corresponding diameter 100 mm along the firstdirection (a first S/D ratio of 0.587), a maximum sag of 10 mm and acorresponding diameter of 60 mm along the second direction (a second S/Dratio of 0.167), and a total curvature of 4.19.

A 64 mm by 1200 mm wide piece of Reflective Polarizer 1 film was cutwith the long direction aligned with the block direction of the film.The grips were set to a distance of 680 mm apart, the inner rollers wereset a distance of 230 mm apart (measured from center to center) and thefilm was loaded into the apparatus with the film passing over the insiderollers and under the outside rollers (the outer rollers centers werepositioned 65 mm outside the inner rollers and travel with innerrollers). The olefin liners were then peeled from the film and threadedout through the rollers. A tension of 15N was applied to the film. Thefilm was heated to 170° C. with a 600 W, 125 mm×125 mm Ceramic type IRheater (supplied by WECO International) located ˜150 mm below the film.The temperature was monitored using an IR temperature sensor with a 12mm spot size. When the film reached the set temperature, the tension wasincreased to 400N and the rollers were moved to a center-to-centerseparation distance of 105 mm. Once the rollers were in place the moldwas plunged (from above) into the film at a rate such that the length offilm contacting the form was as shown in FIG. 32 for one of Conditions1-4 specified in FIGS. 32-34. The positions of the rollers were adjustedso that the free span film length between the point of contact on theform and the point of contact on the roller (corresponding to d1 and d2in FIG. 1E) was as illustrated in FIG. 33. During this process, the filmtension was monitored with two load cells mounted on the grips and thegrips were moved to maintain the tension specified in FIG. 34. The IRheat was maintained on the film during this process. Once the form androllers reached their final positions the part was held over the IRheater for another 60 seconds to help relax any stresses in the film.The heater was then moved away and the film (and form) were allowed tocool for 5 min in ambient air. After cooling, the film tension wasremoved and the rollers and form moved apart to allow the shaped film tobe removed from the machine.

Thicknesses along the first direction (corresponding to thicknessesalong the first curve 3010) and thickness along the second direction(corresponding to thicknesses along the second curve 3020) were measuredusing a Mitutoyo digital micrometer head with a spherical tip mounted ona gage stand and are shown in FIGS. 35-38 for films shaped usingConditions 1-4, respectively.

Descriptions for elements in figures should be understood to applyequally to corresponding elements in other figures, unless indicatedotherwise. Although specific embodiments have been illustrated anddescribed herein, it will be appreciated by those of ordinary skill inthe art that a variety of alternate and/or equivalent implementationscan be substituted for the specific embodiments shown and describedwithout departing from the scope of the present disclosure. Thisapplication is intended to cover any adaptations or variations of thespecific embodiments discussed herein. Therefore, it is intended thatthis disclosure be limited only by the claims and the equivalentsthereof.

All references, patents, and patent applications cited in the foregoingare herein incorporated by reference in their entirety in a consistentmanner. In the event of inconsistencies or contradictions betweenportions of the incorporated references and this application, theinformation in the preceding description shall control.

What is claimed is:
 1. A method of shaping an optical film, the methodcomprising the steps of: disposing the optical film adjacent first andsecond rollers such that a first portion of the optical film contactsthe first roller and a second portion of the optical film contacts thesecond roller, the first and second rollers spaced apart along a firstdirection, the first portion of the optical film having a first widthalong a second direction orthogonal to the first direction; securingopposing first and second ends of the optical film, the first and secondends spaced apart along the first direction, the first and secondportions disposed between the first and second ends; providing a curvedmold surface; and shaping the optical film by contacting the opticalfilm with the curved mold surface while stretching the optical filmalong the first direction, wherein the shaping step comprises keeping athreshold distance between closest first and second points less thanabout the first width, the first point on the optical film contactingthe first roller, the second point on the optical film contacting thecurved mold surface.
 2. The method of claim 1, wherein the shaping stepcomprises changing positions of the first and second ends of the opticalfilm to control a tension in the optical film along the first direction.3. The method of claim 2, wherein the tension is controlled to produce adesired thickness variation in the optical film.
 4. The method of claim1, further comprising heating the optical film to a temperature greaterthan a glass transition temperature of the optical film.
 5. The methodof claim 1, wherein the method results in a shaped optical film having afirst maximum sag along the first direction, and a second maximum sagalong the second direction, the first maximum sag greater than or equalto the second maximum sag, the second maximum sag greater than zero,each location over at least 80% of a total area of the shaped opticalfilm having a reflectance greater than about 80% for normally incidentlight having a same predetermined wavelength and a same firstpolarization state.
 6. The method of claim 1, wherein keeping thethreshold distance between the closest first and second points less thanabout the first width comprises changing a separation distance betweenthe first and second rollers along the first direction.
 7. The method ofclaim 1, further comprising disposing the optical film adjacent thirdand fourth rollers, the third roller adjacent the first roller, thefourth roller adjacent the second roller, wherein the shaping stepfurther comprises changing a separation distance between the third andfourth rollers along the first direction.
 8. The method of claim 7,wherein the third roller is disposed to increase a contact angle of theoptical film with the first roller, and the fourth roller is disposed toincrease a contact angle of the optical film with the second roller. 9.A method of shaping an optical film, the method comprising the steps of:disposing the optical film adjacent first and second rollers such that afirst portion of the optical film contacts the first roller and a secondportion of the optical film contacts the second roller, the first andsecond rollers spaced apart along a first direction, the first portionof the optical film having a first width along a second directionorthogonal to the first direction; securing opposing first and secondends of the optical film, the first and second ends spaced apart alongthe first direction, the first and second portions disposed between thefirst and second ends; providing a curved mold surface; and shaping theoptical film by contacting the optical film with the curved mold surfacewhile stretching the optical film along the first direction, wherein theshaping step comprises changing a separation distance between the firstand second rollers along the first direction to reduce buckling of theoptical film between the first and second rollers and along the seconddirection between and away from longitudinal edges of the optical film.10. The method of claim 9, wherein the optical film has no bucklesbetween the first and second rollers during the shaping step.
 11. Themethod of claim 9, wherein the shaping step comprises keeping athreshold distance between closest first and second points less thanabout the first width, the first point on the optical film contactingthe first roller, the second point on the optical film contacting thecurved mold surface.
 12. The method of claim 9, wherein the shaping stepcomprises changing positions of the first and second ends of the opticalfilm to control a tension in the optical film along the first direction.13. The method of claim 12, wherein the tension is controlled to producea desired thickness variation in the optical film.
 14. A method ofshaping an optical film, the method comprising the steps of: disposingthe optical film adjacent first and second rollers such that a firstportion of the optical film contacts the first roller and a secondportion of the optical film contacts the second roller, the first andsecond rollers spaced apart along a first direction; securing opposingfirst and second ends of the optical film, the first and second endsspaced apart along the first direction, the first and second portionsdisposed between the first and second ends; securing opposing third andfourth ends of the optical film, the third and fourth ends spaced apartalong a second direction orthogonal to the first direction; providing acurved mold surface; and shaping the optical film by contacting theoptical film with the curved mold surface while stretching the opticalfilm, resulting in a curved optical film curved along at least the firstdirection, wherein stretching the optical film during the shaping stepcomprises stretching the optical film along the first direction greaterthan 3 times any stretching along the second direction.
 15. The methodof claim 14, wherein the first portion of the optical film has a firstwidth along the second direction, and wherein the shaping step compriseskeeping a threshold distance between closest first and second pointsless than about the first width, the first point on the optical filmcontacting the first roller, the second point on the optical filmcontacting the curved mold surface.
 16. The method of claim 14, whereinthe shaping step comprises changing a separation distance between thefirst and second rollers along the first direction to reduce buckling ofthe optical film between the first and second rollers and along thesecond direction between and away from longitudinal edges of the opticalfilm.
 17. The method of claim 14, wherein prior to shaping the opticalfilm, the optical film is generally cross shaped and comprises: acentral region disposed between the first and second ends and betweenthe third and fourth ends; first and second end regions extending fromthe central region to the first and second ends, respectively; and thirdand fourth end regions extending from the central region to the thirdand fourth ends, respectively.